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RAID - what does strip size mean?

Posted on 2012-04-10
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Last Modified: 2012-04-11
I consider myself somewhat knowlegable on RAID algorithms but I've just been reading someon's documentation I think I have fallen into a bit of a linguistic trap. So I ask other experts here to see if you fall into the same trap - it is a trick question but I'm not going to flame you if you get it wrong. It's more about reading nglish words than anything else so I'd like my peers input since the documentation says this is "industry standard" but I hadn't noticed it.

So what is strip size? that which is written on each disk before the econtroller moves onto the next one or the sum of all the strip elements in an array?
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Question by:andyalder
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by:n2fc
n2fc earned 200 total points
ID: 37829731
Are you sure you mean "strip?"   Maybe "stripe?"

RAID 0 uses "Striping"... This is the splitting of data across volumes to cut delays in physical access...

Some references for determining optimal stripe size follow:

http://en.wikipedia.org/wiki/Standard_RAID_levels

http://www.overclock.net/t/690318/raid-0-on-hdds-best-stripe-size-goods-bads

http://jonstechbits.com/2008/03/24/raid-stripe-size-what-does-it-mean-and-what-is-the-optimal-stripe-size/
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by:IT-Monkey-Dave
IT-Monkey-Dave earned 100 total points
ID: 37829777
"Stripe" not "strip"  :)

I believe "stripe size" applies to RAID-0 arrays where data is stored across multiple drives but without any fault-tolerance.  If you have a 2-drive RAID-0 setup with a 64KB stripe size, and save a 256KB file, it would use 2 64KB stripes from each of the 2 drives.  That's why if either of those drives fails, you effectively lose half of the saved data, leaving what's left useless.  (Of course there are other variables like the smallest chunk the OS writes or block size, but you get the idea.)

Do I win anything?  Probably not.  At least I didn't resort to The Google!
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by:andyalder
ID: 37829953
Thank you both for falling into the same trap and so verifying I haven't gone dool alley.

I'll post a link to the offending HP document tomorrow and split poinks.
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noxcho earned 200 total points
ID: 37830510
Info from HP:
Stripe size versus strip size
To improve overall performance, RAID controllers break file data up into discrete chunks called "strips" that are distributed one after another across the physical drives in the arrays.

A stripe, on the other hand, is the collection of one set of strips across the physical drives in a logical drive. A stripe’s size is not configured. It is a product of the strip size, the number of physical drives in the logical drive, and the RAID level.

HP Smart Array utilities have traditionally used the term stripe size as a configuration parameter when, in terms of standard RAID definitions, it’s the strip size that’s actually being configured. In order to differentiate between the two, HP documentation has sometimes referred to the RAID stripe as the ¿full stripe¿.

Looks as HP realized that they were using wrong term to name the chunks which are called mistakenly STRIPE by two guys above. So you did not have linguistics problems andy :)
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by:IT-Monkey-Dave
ID: 37830537
Hmm, 20 years in this profession and I've never heard of "strip" in reference to RAID controllers or arrays, only "stripe".  I guess I learned something new.
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by:noxcho
ID: 37831367
It is typical for hardware and software vendors to reconsider their earlier wordings and saying: eh, we were not right in calling this feature so and that feature so. Now it has better naming etc.
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by:andyalder
ID: 37831453
Well spotted noxcho, they even have the audacity to claim most of the industry has always called it "strip" in http://h20000.www2.hp.com/bc/docs/support/SupportManual/c02249094/c02249094.pdf.
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by:noxcho
ID: 37831541
Yeah, they quoted that in 2010 the wording/terming was changed. Page 6:
Most RAID levels are designed to provide increased read performance by distributing, or striping,
data across the set of physical drives that have been configured as a single logical drive. With
striping, each X number of bytes of data of the logical disk is placed on a different physical disk in
the array on a rotating basis. In industry terms, each set of X bytes is called a strip. A stripe is one
complete row of data strips across all of the drives in an array. HP configuration tools have used the
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term stripe size to refer to what most of the industry refers to as the strip size, although this is being
changed in 2010.
The strip size for an array is configurable, and can be set from 16 KB up to 512 KB. In general, using
a larger strip (HP stripe) size delivers higher performance for a RAID array. The Array Configuration
Utility (ACU) determines the largest strip size that can be set for a given logical array based on the
RAID level of the array and the number of physical drives that it contains.
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by:n2fc
n2fc earned 200 total points
ID: 37831903
In other words, they are synonyms, but HP (typically) accuses everyone ELSE of using the "wrong term"... hmmm...
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by:andyalder
ID: 37831980
I've used the ACU dozens of times and didn't spot it.
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