[Lustre-discuss] Clarification on DDN performance best practices

[Kit Westneat]

> 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):
http://ddn.com/index.php?id=48

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.

HTH,
Kit

-- 
---
Kit Westneat
kwestneat at datadirectnet.com
812-484-8485