[Lustre-discuss] Clarification on DDN performance best practices
kwestneat at ddn.com
Mon Apr 13 07:17:32 PDT 2009
> As to this, the tier are organized as something similar to 8+2 RAID6.
> For 8-way data, which is the unit? Sectors? Blocks? In other words, what
> is the stripe data size in KiB with a sector size of 512 vs. a sector
> size of 4KiB?
The S2A directRAID6 is actually based on RAID3, so we use byte striping
instead of block striping. The 4k alignment comes from the physical disk
sector size of 512-bytes (512 * 8 = 4k). The S2A has a cache segment
size, which while independent of the LUN sector size, is sort of similar
in some ways to a block size on a RAID5, though it will never do a
read-modify-write. The cache size can be set between 128k - 2M, and for
Lustre, we usually set it to 1 or 2M, since Lustre currently operates
with 1M messages.
This picture sort of describes from a high level what happens on the
data path (the text is very marketing heavy unfortunately):
If you are going to be at LUG, DDN will have a fair number folks
including myself there, feel free to come say hi. We'll also be talking
at 1 on Friday.
kwestneat at datadirectnet.com
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