Yesterday, I started this week's topic discussing the various areas of exploration to helpunderstand our recent press release of the IBM System Storage SAN Volume Controller and itsimpressive SPC-1 and SPC-2 benchmark results that ranks it the fastest disk system in the industry.
Some have suggested that since the SVC has a unique design, it should be placed in its own category,and not compared to other disk systems. To address this, I would like to define what IBM meansby "disk system" and how it is comparable to other disk systems.
When I say "disk system", I am going to focus specifically on block-oriented direct-access storage systems, which I will define as:
One or more IT components, connected together, that function as a whole, to serve as a target forread and write requests for specific blocks of data.
Clarification: One could argue, and several do in various comments below, that there are other typesof storage systems that contain disks, some that emulate sequential access tape libraries, some that emulate file-systems through CIFS or NFS protocols, and some that support thestorage of archive objects and other fixed content. At the risk of looking like I may be including or excluding such to fit my purposes, I wanted to avoid apples-to-orangescomparisons between very different access methods. I will limit this exploration to block-oriented, direct-access devices. We can explore these other types of storage systems in later posts.
People who have been working a long time in the storage industry might be satisfied by this definition, thinkingof all the disk systems that would be included by this definition, and recognize that other types of storage liketape systems that are appropriately excluded.
Others might be scratching their heads, thinking to themselves "Huh?" So, I will provide some background, history, and additional explanation. Let's break up the definition into different phrases, and handle each separately.
- read and write requests
Let's start with "read and write requests", which we often lump together generically as input/output request, or just I/O request. Typically an I/O request is initiated by a host, over a cable or network, to a target. The target responds with acknowledgment, data, or failure indication. A host can be a server, workstation, personal computer, laptop or other IT device that is capable of initiating such requests, and a target is a device or system designed to receive and respond to such requests.
(An analogy might help. A woman calls the local public library. She picks up the phone, and dials the phone number of the one down the street. A man working at the library hears the phone ring, answers it with "Welcome to the Public Library! How can I help you?" She asks "What is the capital city of Ethiopia?" and replies "Addis Ababa." and hangs up. Satisfied with this response, she hangs up. In this example, the query for information was the I/O request, initiated by the lady, to the public library target)
Today, there are three popular ways I/O requests are made:
- CCW commands over OEMI, ESCON or FICON cables
- SCSI commands over SCSI, Fibre Channel or SAS cables
- SCSI commands over Ethernet cables, wireless or other IP communication methods
- specific blocks of data
In 1956, IBM was the first to deliver a disk system. It was different from tape because it was a "direct access storage device" (the acronym DASD is still used today by some mainframe programmers). Tape was a sequential media, so it could handle commands like "read the next block" or "write the next block", it could not directly read without having to read past other blocks to get to it, nor could it write over an existing block without risking overwriting the contents of blocks past it.
The nature of a "block" of data varies. It is represented by a sequence of bytes of specific length. The length is determined in a variety of ways.
- CCW commands assume a Count-Key-Data (CKD) format for disk, meaning that tracks are fixed in size, but that a track can consist of one or more blocks, and can be fixed or variable in length. Some blocks can span off the end of one track, and over to another track. Typical block sizes in this case are 8000 to 22000 bytes.
- SCSI commands assume a Fixed-Block-Architecture (FBA) format for disk, where all blocks are the same size, almost always a power of two, such as 512 or 4096 bytes. A few operating systems, however, such as i5/OS on IBM System i machines, use a block size that doesn't follow this power-of-two rule.
- one or more IT components
You may find one or more of the following IT components in a disk system:
- customized or general-purpose processing chips
- memory, such as RAM, Flash, or similar
- batteries and/or other power supply
- Host attachment cards or ports
- motorized platter(s) covered in magnetic coating with a read/write head to move over its surface. These are often referred to as Hard Disk Drive (HDD) or Disk Drive Modules (DDM), and are manufacturedby companies like Seagate or Hitachi Global Storage Technologies.
A set of HDD can be accessed individually, affectionately known as JBOD for Just-a-bunch-of-disk, or collectively in a RAID configuration.
Memory can act as the high-speed cache in front of slower storage, or as the storage itself. For example, the solid state disk that IBM announced last week is entirely memory storage, using Flash technology.
Lately, there are two popular packaging methods for disk systems:
- Monolithic -- all the components you need connected together inside a big refrigerator-sized unit, with options to attach additional frames. The IBM System Storage DS8000, EMC Symmetrix DMX-4 and HDS TagmaStore USP-V all fit this category.
- Modular -- components that fit into standard 19-inch racks, often the size of the vegetable drawer inside a refrigerator, that can be connected externally with other components, if necessary, to make a complete disk system. The IBM System Storage DS6000, DS4000, and DS3000 series, as well as our SVC and N series, fall into this category.
Regardless of packaging, the general design is that a "controller" receives a request from its host attachment port, and uses its processors and cache storage to either satisfy the request, or pass the request to the appropriate HDD,and the results are sent back through the host attachment port.
In all of the monolithic systems, as well as some of the modular ones, the controller and HDD storage are contained in the same unit. On other modular systems, the controller is one system, and the HDD storage is in a separate system, and they are cabled together.
- serve as a target
The last part is that a disk system must be able to satisfy some or all requests that come to it.
(Using the same analogy used above, when the lady asked her question, the guy at the public library knew the answer from memory, and replied immediately. However, for other questions, he might need to look up the answer in a book, do a search on the internet, or call another library on her behalf.)
Some disk systems are cache-only controllers. For these, either the I/O request is satisfied as a read-hit or write-hit in cache, or it is not, and has to go to the HDD. The IBM DS4800 and N series gateways are examples of this type of controller.
Other systems may have controller and disk, but support additional disk attachment. In this case, either the I/O request is handled by the cache or internal disk, or it has to go out to external HDD to satisfy the request. IBM DS3000 series, DS4100, DS4700, and our N series appliance models, all fall into this category.
So, the SAN Volume Controller is a disk system comprising of one to four node-pairs. Each node is a piece of IT equipment that have processors and cache. These node-pairs are connected to a pair of UPS power supplies to protect the cache memory holding writes that have not yet been de-staged. The combination of node-pairs and UPS acting as a whole, is able to serve as a target to SCSI commands sent over Fibre Channel cables on a Storage Area Network (SAN). To read some blocks of data, it uses its internal cache storage to satisfy the request, and for others, it goes out to external disk systems that contain the data required. All writes are satisfied immediately in cache on the SVC, and later de-staged to external disk when appropriate.
As of end of 2Q07, having reached our four-year anniversary for this product, IBM has sold over 9000 SVC nodes, which are part of more than 3100 SVC disk systems. These things are flying off the shelves, clocking in a 100% YTY growth over the amount we sold twelve months ago. Congratulations go to the SVC development team for their impressive feat of engineering that is starting to catch the attention of many customers and return astounding results!
So, now that I have explained why the SVC is considered a disk system, tomorrow I'll discuss metrics to measure performance.
technorati tags: IBM, SVC, HDD, DDM, DS4800, SVC, SAN Volume Controller, EMC, HDS, HP, DS4100, DS4700, Flash, RAM, solid-state, disk, system, controller, array, RAID, I/O, IO, request, read, write,
Continuing my business trip through Asia, I have left Chengdu, China, and am now in Kuala Lumpur, Malaysia.
On Sunday, a colleague and I went to the famous Petronas Twin Towers, which a few years ago were officially the tallestbuildings in the world. If you get there early enough in the day, and wait in line for a few hours, you can get a ticket permitting you to go up to the "Skybridge" on the 41st floor that connects the two buildings. The views are stunning, and I am glad to have done this.(If you are afraid of heights, get cured by facing your fears with skydiving)
You would think that a question as simple as "Which is the tallest building in the world?" could easily be answered, given that buildings remain fixed in one place and do not drastically shrink or get taller over time or weather conditions, and the unit of height, the "meter", is an officially accepted standard in all countries, defined as the distance traveled by light in absolute vacuum in 1/299,792,458 of a second.
The controversy stems around two key areas of dispute:
- What constitutes a building?
A building is a structure intended for continuous human occupancy, as opposed to the dozens ofradio and television broadcasting towers which measure over 600 meters in height. The Petronas Twin Towers is occupied by a variety of business tenants and would qualify as a building. Radio and Television towers are not intended for occupation, and should not be considered.
- Where do you start measuring, and where do you stop?
Since 1969, the height was generally based on a building's height from the sidewalk level of the main entrance to the architectural top of the building. The "architectural top" included towers, spires (but not antennas), masts or flagpoles. Should the measurements be only to the top to the highest inhabitable floor?
What if the building has many more floors below ground level? What if the building exists in a body of water, should sidewalk level equate to water level, and at low tide or high tide? (Laugh now, but this might happen sooner than you think!)
To bring some sanity to these comparisons, the Council on Tall Buildings and Urban Habitat has tried to standardize the terms and definitions to makecomparisons between buildings fair. Why does all this matter whose building is tallest? It matters in twoways:
- People and companies are willing to pay more to be a tenant in tall towers, affording a luxurious bird's-eyeview to impress friends, partners and clients, and so the rankings can influence purchase or leasing prices of floorspace in these buildings.
- Architects and engineers involved in building these structures want to list these on their resume.These buildings are an impressive feat of engineering, and the teams involved collaborate in a global mannerto accomplish them. If an architecture or engineeering company can build the world's tallest building, you can trust themto build one for you. The rankings can help drive revenues in generating demand for services and offerings.
What does any of this have to do with storage? Two weeks ago, IBM and the Storage Performance Councilanswered the question "Which is the fastest disk system?" with apress release. Customers thatcare about performance of their most mission critical applications are often willing to pay a premium to run theirapplications on the fastest disk system, and the IBM System Storage SAN Volume Controller, built through aglobal collaboration of architects and engineers across several countries, is (in my opinion at least) an impressive feat of storage engineering.
EMC bloggerChuck Hollis was the first to question the relevance of these results, and I failed to "turn the other cheek" and responded accordingly. The blogosphere erupted, with more opinions piled on by others, many from EMC andIBM, found in comments on these posts or other blogs, some have since been retracted or deleted, while othersremain for historical purposes.
At the heart of all this opinionated debate, lies a few areas of exploration:
- What constitutes a "disk system"? What should or should not be considered for comparison?
- What metrics should be used to measure performance? What is a version of the "meter" everyone can use?
- How should the measurements occur? Who should perform them?
- Do the measurements provide sufficient value for the purpose of aiding the purchase decision making process?
I will try to address some of these issues in a series of posts this week.
technorati tags: IBM, KL, Kuala Lumpur, Malaysia, Petronas, Twin Towers, SkyBridge, tallest, building, structure, tower, fasted, disk, system, SVC, SAN Volume Controller, EMC, Chuck Hollis, SPC, Storage Performance Council
For those in the US, a comedian named Carlos Mencia has a great TV show, Mind of Mencia
and one of my favorite segments is "Why the @#$% is this news!" where he goes about showingblatantly obvious things that were reported in various channels.
So, when I saw that IBM once again, for the third year in a row, has the fastest disk system,the IBM System Storage SAN Volume Controller (SVC), based on widely-accepted industry benchmarksrepresenting typical business workloads, I thought, "Do I really want to blog about this,and sound like a broken record, repeating my various statements of the past of how great SVC is?" It's like reminding people that IBM hashad the most US patents than any other company, every year, for the past 14 years.
(Last year, I received comments fromWoody Hutsell, VP of Texas Memory Systems,because I pointed out that their "World's Fastest Storage"® cache-only system, was not as fast as IBM's SVC.You can ready my opinions, and the various comments that ensued, hereand here. )
That all changed when EMC uber-blogger Chuck Hollis forgot his own Lessons in Marketingwhen heposted his rantDoes Anyone Take The SPC Seriously?That's like asking "Does anyone take book and movie reviews seriously?" Of course they do!In fact, if a movie doesn't make a big deal of its "Two thumbs up!" rating, you know it did not sitwill with the reviewers. It's even more critical for books. I guess this latest news from SPC reallygot under EMC's skin.
For medium and large size businesses, storage is expensive, and customers want to do as much research as possible ahead of time to make informed decisions. A lot of money is at stake, and often, once you choose a product, you are stuckwith that vendor for many years to come, sometimes paying software renewals after only 90 days, and hardware maintenance renewals after only a year when the warranty runs out.
Customers shopping for storage like the idea of a standardized test that is representative, so they can compare one vendor's claims with another. The Storage Performance Council (SPC), much like the Transaction Processing Performance Council (TPC-C) for servers, requires full disclosure of the test environment so people can see what was measured and make their own judgement on whether or not it reflects their workloads. Chuck pours scorn on SPC but I think we should point to TPC-C as a great success story and ask why he thinks the same can't happen for storage? Server performance is also a complicatedsubject, but people compare TPC-C and TPC-H benchmarks all the time.
Note: This blog post has been updated. I am retracting comments that were unfair generalizations. The next two paragraphs are different than originally posted.
Chuck states that "Anyone is free, however, to download the SPC code, lash it up to their CLARiiON, and have at it." I encourage every customer to do this with whatever disk systems they already have installed. Judge for yourself how each benchmark compares to your experience with your application workload, and consider publishing the results for the benefit of others, or at least send me the results, so that I can understand better all of these"use cases" that Chuck talks about so often. I agree that real-world performance measurements using real applications and real data are always going to be more accurate and more relevant to that particular customer. Unfortunately, there are little or no such results made public. They are noticeably absent. With thousands of customers running with storage from all the major storage vendors, as well as storage from smaller start-up companies, I would expect more performance comparison data to be readily available.
In my opinion, customers would benefit by seeing the performance results obtained by others. SPC benchmarks help to fill this void, to provide customers who have not yet purchased the equipment, and are looking for guidance of which vendors to work with, and which products to put into their consideration set.
Truth is, benchmarks are just one of the many ways to evaluate storage vendors and their products. There are also customer references, industry awards, and corporate statements of a company's financial health, strategy and vision.Like anything, it is information to weigh against other factors when making expensive decisions. And I am sure the SPC would be glad to hear of any suggestions for a third SPC-3 benchmark, if the first two don't provide you enough guidance.
So, if you are not delighted with the performance you are getting from your storage now, or would benefit by having even faster I/O, consider improving its performance by adding SAN Volume Controller. SVC is like salt or soy sauce, it makes everything taste better. IBM would be glad to help you with a try-and-buy or proof-of-concept approach, and even help you compare the performance, before and after, with whatever gear you have now. You might just be surprised how much better life is with SVC. And if, for some reason, the performance boost you experience for your unique workload is only 10-30% better with SVC, you are free to tell the world about your disappointment.
technorati tags: Carlos Mencia, Mind of Mencia, IBM, system, storage, SVC, SAN Volume Controller, Storage Performance Council,SPC, benchmarks, Texas Memory Systems, Woody Hutsell, EMC, Chuck Hollis, movie, book, reviews, awards, salt, soy sauce
Wrapping up my week's discussion on Business Continuity, I've had lots of interest in myopinion stated earlier this week that it is good to separate programs from data
, and thatthis simplifies the recovery process, and that the Windows operating system can fit in a partition as small asthe 15.8GB solid state drive
we just announced for BladeCenter. It worked for me, and I will use this post to show you how to get it done.
Disclaimer: This is based entirely on what I know and have experienced with my IBM Thinkpad T60 running Windows XP, and is meant as a guide. If you are running with different hardware or different operating system software, some steps may vary.
(Warning: Windows Vista apparently handles data, Dual Boot, andPartitions differently. These steps may not work for Vista)
For this project, I have a DVD/CD burner in my Ultra-Bay, a stack of black CDs and DVDs, and a USB-attached 320GB external disk drive.
- Step 0 - Backup your system
I find it amusing that this is ALWAYS the first step, but nobody provides any instruction.I will assume we start with a single C: drive with an operational Windows operating system, intermixed programs and data. If you have a Thinkpad, you should have "IBM Rescue and Recovery" program already installed, but is probably down-level. Mine was version 2.0 -- Yikes! Download IBM Rescue and Recovery Version 4.0 for Windows XP and Windows 2000,and reboot to make it fully installed.
Make TWO backups. First, make a bootable rescue CD and backup to several DVDs. Second, backup to a large external 320GB USB-attached disk drive. IBM Rescue and Recovery does compression, so a 60GB drive that is mostly full might take about 8-10 DVDs, have plenty on hand. If you have to recover, boot from CD, and restore from the USB-attached drive. If that doesn't work, you have the DVDs just in case.
If you are suitably happy with your backups, you are ready for step 1. For added protection, you can use a Linux LiveCD to backup your entire drive. I suggestSysRescCD, which is designed to be a rescue CD and can do backups and restores.
First, figure out if your drive is "hda" or sda. The "dmesg" command below shows that mine is "sda", with output like this:
tpearson@tpearson:~$ dmesg | grep [hs]d[ 7.968000] SCSI device sda: 117210240 512-byte hdwr sectors (60012 MB)[ 7.968000] sda: Write Protect is offI like to backup the master boot record to one file, and then the rest of the C: drive to a series of 690MB compressed chunks. These can be directed to the USB-attached drive, and then later burned onto CDrom, or pack 6 files per DVD.Most USB-attached drives are formatted to FAT32 file system, which doesn't support any chunks greater than 2GB, so splitting these up into 690MB is well below that limit.
[ 7.968000] sda: Mode Sense: 00 3a 00 00[ 7.968000] SCSI device sda: write cache: enabled, read cache: enabled
dd if=/dev/sda of=/media/USBdrive/master.MBR bs=512 count=1dd if=/dev/sda1 conv=sync,noerror | gzip -c | split -b 690m - /media/USBdrive/master.gz.To recover your system, just reverse the process:
cat /media/USBdrive/master.gz.* | gzip -dc | dd of=/dev/sda1dd if=/media/USBdrive/master.MBR of=/dev/sda bs=512 count=1You can learn more about these commands here and here.
- Step 1 - Defrag your C: drive
From Windows, right-click on your Recycle Bin and select "Empty Recycle Bin".
Click Start->Programs->Accessories->System Tools->Disk Defragmenter. Select C: drive and push the Analyze button. You will see a bunch of red, blue and white vertical bars. If there are any greenbars, we need to fix that. The following worked for me:
- Right-click "My Computer" and select Properties. Select Advanced, then press "Settings" buttonunder Performance. Select Advanced tab and press the "Change" button under Virtual Memory.Select "No Paging File" and press the "Set" button. Virtual memory lets you have many programs open, moving memory back and forth between your RAM and hard disk.
- Click Start->Control Panel->Performance and Maintenance->Power Options. On the Hibernate tab,make sure the "Enable Hibernation" box is un-checked. I don't use Hibernate, as it seems likeit takes just as long to come back from Hibernation as it does to just boot Windows normally.
- Reboot your system to Windows.
If all went well, Windows will have deleted both pagefile.sys and hiberfil.sys, the twomost common unmovable files, and free up 2GB of space. You can run just fine without either of these features, but if you want them back, we will put them back on Step 6 below.
Go back to Disk Defragmenter, verify there are no green bars, andproceed by pressing the "Defragment" button. If there are still some green bars,you can proceed cautiously (you can always restore from your backup right?), or seek professional help.
- Step 2 - Resize your C: drive
When the defrag is done, we are ready to re-size your file system. This can be done with commercial software like Partition Magic.If you don't have this, you can use open source software. Burn yourself the Gparted LiveCD.This is another Linux LiveCD, and is similar to Partition Magic.
Either way, re-size the C: drive smaller. In theory, you can shrink it down to 15GB if this is a fresh install of Windows, and there is no data on it. If you have lots of data, and the drive wasnearly full, only resize the C: drive smaller by 2GB. That is how much we freed upfrom the unmovable files, so that should be safe.
You could do steps 2 and 3 while you are here, but I don't recommend it. Just re-size C:press the "Apply" button, reboot into Windows, and verify everything starts correctly before going to the next step.
- Step 3 - Create Extended Paritition and Logical D: drive
You can only have FOUR partitions, either Primary for programs, or Extended for data. However, theExtended partition can act as a container of one or more logical partitions.
Get back into Partition Magic or Gparted program, and in the unused space freed up from re-sizing inthe last step, create a new extended/logical partition. For now, just have one logical inside theextended, but I have co-workers who have two logical partitions, D: for data, and E: for their e-mailfrom Lotus Notes. You can always add more logical partitions later.
I selected "NTFS" type for the D: drive. In years past, people chose the older FAT32 type, but this has some limitations, but allowed read/write capability from DOS, OS/2, and Linux.Windows XP can only format up to 32GB partitions of FAT32, and each file cannot be bigger than 2GB.I have files bigger than that. Linux can now read/write NTFS file systems directly, using the new NTFS-3Gdriver, so that is no longer an issue.
- Step 4 - Format drive D: as NTFS
Just because you have told your partitioning program that D: was NTFS type, you stillhave to put a file system on it.
Click Start->Control Panel->Performance and Maintenance->Computer Management. Under Storage, select Disk Management. Right-click your D: drive and choose format.Make sure the "Perform Quick Format" box is un-checked, so that it peforms slowly.
- Step 5 - Move data from C: to D: drive
Create two directories, "D:\documents" and "D:\notes\data", either through explorer, or in a commandline window with "MKDIR documents notes\data" command.
Move files from c:\notes\data to d:\notes\data, and any folder in your "My Documents" over to d:\documents.
(If you have more data than the size of the D: drive, copy over what you can, run another defrag, resize your C: drive even smaller with Partition Magic or Gparted, Reboot, verify Windows is still working,resize your D: bigger, and repeat the process until you have all of your data moved over.)
To inform Lotus Notes that all of your data is now on the D: drive, use NOTEPAD to edit notes.ini and change the Directory line to "Directory=D:\notes\data". If you have a special signature file, leave it in C:\notes directory.
Once all of your data is moved over to D:\documents, right-click on "My Documents" and select Properties. Change the target to "D:\documents" and press "Move" button. Now, whenever you select "My Documents", youwill be on your D: drive instead.
- Step 6 - Take A Fresh Backup
If you use IBM Tivoli Storage Manager, now would be a good time to re-evaluate your "dsm.opt" file that listswhat drives and sub-directories to backup. Take a backup, and verify your data is being backed up correctly.
With the USB-attached, backup both C: and D: drives. I leave my USB drive back in Tucson. For a backup copywhile traveling, go to IBM Rescue and Recovery and take a C:-only backup to DVD. Make sure D: drive box is un-checked. Now, if I ever need to reinstall Windows, because of file system corruption or virus, I can do this from my one bootable CD plus 2 DVDs, which I can easily carry with me in my laptop bag, leaving all my data on the D: drive in tact.
In the worst case, if I had to re-format the whole drive or get a replacement disk, I can restore C: and thenrestore the few individual data files I need from IBM Tivoli Storage Manager, or small USB key/thumbdrive,delaying a full recovery until I return to Tucson.
Lastly, if you want, reactivate "Virtual Memory" and "Hibernation" features that we disabled in Step 1.
As with Business Continuity in the data center, planning in this manner can help you get back "up and running"quickly in the event of a disaster.
technorati tags: IBM, Business Continuity, Windows, XP, BladeCenter, solid, state, disk, backup, Linux, sysresccd, LiveCD, dd, gzip, split, Tivoli, Storage Manager, USB, Lotus Notes, NTFS, NTFS-3G, FAT32, primary, extended, logical, partition, magic, gparted
Continuing this week's theme on Business Continuity, I will use this post to discuss this week'sIBM solid state disk announcement
.This new offering provides a new way to separate programs from data, to help minimizedowntime and outages normally associated with disk drive failures.
Until now, the method most people used to minimize the amount of data on internalstorage was to use disk-less servers with Boot-Over-SAN, however, not all operating systems, and not all disk systems, supported this.
In April, the BladeCenter HS21 XM blade server introduced the option to have oneIBM 4GB Flash Memory Device that used the USB2.0 protocol. The 4GB drive can be usedto boot 32-bit and 64-bit versions of Linux, such as Red Hat Enterprise Linux (RHEL) and SUSE Linux Enterprise Server (SLES)), but not Windows. Linux is incredibly small operating system. You can bootversions from a USB key/thumbdrive (64MB) or CD (700MB) image, so it makes sense that a 4GB flash drive based on USB protocol was a good fit for Linux.
Windows, however, is not supported, because of the small 4GB size and USB protocol limitations. For Windows, you would add a SAS drive, you boot from this hard drive, and use the 4GB Flash drive for data only.
So what's new this time? Here's a quick recap of July 17 announcement. For the IBM BladeCenter HS21 XM blade servers, new models of internal "disk" storage:
- Single drive model
A single 15.8GB solid-state disk drive, based on SATA protocol. In addition to theLinux operating systems mentioned above, the capacity and SATA protocols allowsyou to boot 32-bit and 64-bit versions of Windows 2003 Server R2, with plans in placeto other platforms in the future, such as VMware. I am able to run my laptop Windows with only 15GB of C: drive, separating my data to a separate D: partition, so this appears to be a reasonable size.
- Dual drive model
The dual drive fits in the space of a single 2.5-inch HDD drive bay.You can combine these in either RAID 0 or RAID 1 mode.
- RAID 0 gives you a total of 31.6GB, but is riskier. If you lose either drive,you lose all your data. Michael Horowitz of Cnet covers the risks of RAID zerohere andhere.However, if you are just storing your operating system and application, easily re-loadable from CD or DVD in the case of loss, then perhaps that is a reasonable risk/benefit trade-off.
- RAID 1 keeps the capacity at 15.8GB, but provides added protection. If you loseeither drive, the server keeps running on the surviving drive, allowing you to schedule repair actions when convenient and appropriate. This would be the configuration I would recommend for most applications.
Until recently, solid state storage was available at a price premium only. Flash prices have dropped 50% annually while capacities have doubled. This trend is expected to continue through 2009.
According to recent studies from Google and Carnegie Mellon, hard drives fail more oftenthan expected. By one account, conventional hard disk drives internal to the server account for as much as 20-50% of component replacements.IBM analysis indicates that the replacement rate of a solid state drive on a typical blade server configuration is only about 1% per year, vs. 3% or more mentionedin the these studies for traditional disk drives.
Flash drives use non-volatile memory instead of moving parts, so less likely to break down during high external environmental stress conditions, like vibration and shock, or extreme temperature ranges (-0C° to +70°C) that would make traditional hard disks prone to failure.This is especially important for our telecommunications clients, who are always looking for solutions that are NEBS Level 3 compliant.
Last year, I mentioned that flash drives could provide only a limited number of write and erase cycles, but today's new advances in wear-leveling algorithms have nearly eliminated this limitation.
As with any SATA drive, performance depends on workload.Solid state drives perform best as OS boot devices, taking only a few secondslonger to boot an OS than from a traditional 73GB SAS drive. Flash drives also excel in applications featuring random read workloads, such as web servers. For random and sequential write workloads, use SAS drives instead for higher levels of performance.
Part of IBM's Project Big Green, these flash drives are very energy efficient. Thanks to sophisticated power management software, the power requirement of the solid state drive can be 95 percent better than that of a traditional 73GB hard disk drive. These 15.8GB drives use only 2W per drive versus as much as 10W per 2.5” hard drive and 16W per 3.5” hard drive. The resulting power savings can be up to 1,512 watts per server rack, with 50% heat reduction.
So, even though this is not part of the System Storage product line, I am very excitedfor IBM. To find out if this will work in your environment, go to the IBM Server Provenwebsite that lists compatability with hardware, applications and middleware, or review the latest Configuration and Options Guide (COG).
technorati tags: IBM, Business, Continuity, solid, state, flash, disk, drive, announcement, blade, server, BladeCenter, H21, XM, 4GB, Flash, Memory, Device, USB2.0, Linux, RedHat, RHEL, Novell, SUSE, SLES, Windows, Project, Big Green, SATA, SAS, energy, efficient, efficiency, performance, NEBS, telecommunications, boot-over-SAN, Google, Carnegie Mellon, study, Vmware