Random question about allocation size

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Deslok

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Jul 15, 2015
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I'm setting up some new storage servers and i'm looking at capacities north of 32TB, I know this means I have to use 16KB clusters at minimum but is there any advantage to matching my cluster size to the raid stripe size(64kb)
 

cesmith9999

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Mar 26, 2013
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There is some advantage at speed. But it is in the single digits in improvement.

The real gotcha is running any applications that depend on the vss snapshots. This includes deduplication and backup software. They will simply not work with an allocation greater than 16k. This is vss limitation.

Chris
 

Deslok

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Jul 15, 2015
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That was my hunch, fortunately nothing is running dedup directly(it's an iscsi target for hyper-v) so all of that is abstracted away since each VM will have it's own cluster size ect. Thanks.
 

i386

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Mar 18, 2016
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The stripe size how large your io has to be to get advantages from the raid.

With striped raids (0, and mirrored varaintions like like 10) you will get better read and writes when your io is larger than 64kb.
With parity raids (5,6, and mirrored varaintions like 50,60) you will get read advantages when your io is bigger than the stripe size, but no advantages for writing.

Without any caching this would be very noticable, but we have nowadays controllers with 1+ gb ram or features like cachecade/maxcache that can improve performance drastically. Especially with parity raids.
 

Deslok

Well-Known Member
Jul 15, 2015
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The stripe size how large your io has to be to get advantages from the raid.

With striped raids (0, and mirrored varaintions like like 10) you will get better read and writes when your io is larger than 64kb.
With parity raids (5,6, and mirrored varaintions like 50,60) you will get read advantages when your io is bigger than the stripe size, but no advantages for writing.

Without any caching this would be very noticable, but we have nowadays controllers with 1+ gb ram or features like cachecade/maxcache that can improve performance drastically. Especially with parity raids.
Good thing it's all solid state! 2x500 for boot and 14x2tb for storage in the raid 6!