This is my first post and I will be talking about Solid State Drivers (a.ka. SSDs) and its applications on IBM's Power Systems.
SSDs has been on the news for quite a while now, however IBM haven't announced it until mid-2009 its transition to SSD technology on some of its products. Not much time ago IBM finished its transition to SAS technology - thus ending the SCSI-era on Power Systems.
But, what the heck is a SSD drive? As the name sounds, it's solid - ok - but, isn't regular SCSI/SAS disk drivers 'solid' too? Of course they're, so what's the difference? Why do they cost so much? What are the advantages? Let take each question down - one by one.
1. Differences from SCSI/SAS disk drivers
As we all know, SCSI/SAS disks have 'mobile' parts. A magnetic disk, which spins at a very fast rate, which requires a micro-engine. While the magnetic disk spins, a read/write head that is responsible for ...guess what? :-) Yes, the read and the write of data into the magnetic disk.
Bad news - the 'head' has to move up and down the disk to read/write data, depending on where it is physically located. This takes a loooong time to be accomplished and is a performance killer.
SSD drives do not have mobile parts, it's a single block-piece-of-hardware - just like a piece of RAM. Internally it is made of a lot of transistors.
Good news - No seek time! It works just like a RAM - but it isn't volatile.
2. IBM Power SSD Technology
IBM uses a SSD technology named of SLC (Single Level Cell) flash memory technology (I won't be entering deep on the technology). It still costs about 40x more per GB versus its old friend HDD, but prices are coming down very fast, so expect to see more in a near future.
Although SSD provides very fast I/O its life is very limited - each single cell supports about 1.000.000 (one million) writes. But it brings other benefits, such as:
- Wear leveling - writes are spread around - ensure that some cells are not over worked and wear out;
- Bad block relocation;
- Over Provisioned - 69Gb available, but 128Gb used - this means that the driver is actually a 128Gb driver, but for safety reasons it has only 69Gb usable. Around 85% of redundancy.
Watts Required for 135K IOPS performance
3. Performance - Where it makes the difference
SSD drivers are ultra high "performatic" drivers. It's easy to say, but where are the numbers? See bellow:
|100% random 4Kb Reads||29,000 IOPS||26,234 IOPS||60,837 IOPS|
|100% random 4Kb Writes||21,000 IOPS||16,669 IOPS||58,068 IOPS|
|Mixed reads+writes 4 KB||14,000 IOPS||16,110 IOPS||59,359 IOPS|
|Sequential reads large block||240 MB/s||240 MB/s||666 MB/s|
|Sequential writes large block||125 MB/s||124,5 MB/s||302 MB/s|
As you can see, the adapter can easily become a bottleneck.
Entry marked for SSD drivers are very high IOPS applications, where existing customers use many physical disks to achieve a better performance, and yet, with a lot of unused capacity. One single SSD driver can potentially replace 100+ HDDs.
4. More Information
Further information about SSD drivers and AIX + Power Systems can be found at:
AIX Wiki - Solid State Driver
Driving Business Value on Power Systems with Solid State Drives
See you on my next post!