Recommend me RAID 6 stripe size (storage server)

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rmd3003

Limp Gawd
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Let's say I'm running media server with 12 2TB drives (total 24TB) in RAID6. Data is stored like this (mix of large and small files):

FOLDER1--
FILE1.ISO 10GB
FILE1.TXT 5KB

FOLDER2--
FILE2.ISO 8GB
FILE2.TXT 1KB
FILE2.JPG 100KB

What would be the best stripe size in this case. It will be "write once" / "read a lot" single GPT volume on Windows Server 2008 R2. Controller is LSI 9260 with 512MB cache. I was thinking about 512KB stripe but I could be wrong.

Thank you.
 
You should not pick a too high stripesize for RAID5 or RAID6 since doing small I/O would then come at a high penalty.

With 512K stripesize and 12 disks in RAID6, the full block size would be 512K * 10 (12 - 2) = 5MiB. That means that to modify or write a few kilobytes, you have to:
- read the full stripe block (5MiB)
- calculate new parity for the stripe block (5MiB XOR)
- write the full stripe block (5MiB)

With a lower stripesize, small writes would be a bit faster. Note that RAID5 and RAID6 performance is much different from RAID0/1 and combinations (0+1 or 1+0) in this regard.

128KiB is a decent default stripesize. Note that alignment is also important. Windows 7 uses 2048 sector offset or 1MiB alignment. Your fill stripe block SHOULD be optimized for this:

- full stripe block = 128KiB = 1MiB / 128K = GOOD
- full stripe block = 512KiB = 1MiB / 512K = GOOD
- full stripe block = 768KiB = 1MiB / 768K = not so good
- full stripe block = 2MiB = 1MiB / 2MiB = better than above

Full stripe block is the number of DATA disks (so total disks minus parity disks) multiplied with the stripesize.
 
rmd3003 said:
What would be the best stripe size in this case. It will be "write once" / "read a lot" single GPT volume on Windows Server 2008 R2. Controller is LSI 9260 with 512MB cache. I was thinking about 512KB stripe but I could be wrong.
Click to expand...

512KB is an excellent choice for the usage you have described.
 
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