Inside System Storage -- by Tony Pearson

Tony Pearson Tony Pearson is a Master Inventor and Senior IT Specialist for the IBM System Storage product line at the IBM Executive Briefing Center in Tucson Arizona, and featured contributor to IBM's developerWorks. In 2011, Tony celebrated his 25th year anniversary with IBM Storage on the same day as the IBM's Centennial. He is author of the Inside System Storage series of books. This blog is for the open exchange of ideas relating to storage and storage networking hardware, software and services. You can also follow him on Twitter @az990tony.
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Comments (8)

1 localhost commented Trackback

So, by your definition, is a netapps filer a disk system? What about a straight NAS? The first allows for block (specific scsi) and file level access, and the second does file level only.

2 localhost commented Trackback

Exactly! NetApp, and by extension IBM System Storage N series, that support FCP and iSCSI access, fall into this definition of "disk system". Applications that read/write specific blocks of data, either with applications like databases that access blocks directly, or OS-specific file systems that write directories, files and other internal information on specific blocks, would be able to use these in either FCP or iSCSI mode. Thus, these FCP/iSCSI-enabled boxes could be compared with other FCP/iSCSI-enabled boxes.<div>&nbsp;</div> Devices that only supported file-level protocols, NFS, CIFS, HTTP or FTP, would not provide this support. Reading 4096 bytes of a file is different than reading 4096 bytes of a block, because the first involves additionally reading various directory structures and writing various statistics that file systems do above the layer of block level devices.

3 localhost commented Permalink

Some question about the SVC:<div>&nbsp;</div> qoute of blog: All writes are satisfied immediately in cache on the SVC, and later de-staged to external disk when appropriate.<div>&nbsp;</div> But there is an option to disable the cache of the vdisks. So when do you want to do this?<div>&nbsp;</div>

4 localhost commented Trackback

"serve as a target" question.<div>&nbsp;</div> Could you please take a moment to restate or clarify what differentiates the two types of targets, say a DS4800 from a DS4700? Is the difference merely a physical separation of cache from HDDs on an enclosure level?

5 localhost commented Trackback

I have had several people say that my "definition" eliminates other storage that may contain HDD, such as virtual tape libraries VTL, NAS-only filers, and archive/compliance storage like the IBM DR550, IBM N series with SnapLock, and EMC Centera. I made an effort to define disk systems broad enough that they included the majority of disk systems that support business applications, either as raw logical volumes, or a variety of file systems from each operating system, that could replace one for the other in such comparisons.<div>&nbsp;</div> It would be more fair to compare VTL with physical tape libraries, commands such as read-next-block and write-next-block are handled in a similar manner between these two.<div>&nbsp;</div> It would be more fair to compare NAS-only filers with combinations of OS-specific file systems plus disk system. How fast an application and read or write files, create files, delete files, and move or copy files can be measured between NAS and other file systems.<div>&nbsp;</div> It would be more fair to compare archive/compliance storage from applications that write to such devices. How quickly such a device can storage an object, whether it is a row in a database table, an e-mail attachment, or an entire file, can be compared with other similar devices.<div>&nbsp;</div> So, while comparisons can be made in these other areas, different metrics and measurement approaches are required.<div>&nbsp;</div>

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