[Lustre-discuss] stripe offset and hot-spots

[John White]

Hello Folks,
	So I'm trying to get a theoretical understanding of stripe offsets in lustre.  As I understand it, the default offset set to 0 results in all writes beginning at OSS0-OST0.  With a default stripe of 4, doesn't this lead to massive hotspots on OSS0-OST[0-3] (unless *all* writes are consistently large)?

	With our setup, we have 4 OSTs per OSS (well, the last OSS has 3, but that's not important right now).  This would appear, in theory, to put OSS0 in a very hot situation.

	That said, I wonder how efficient a solution setting the stripe offset of the root of the file system to -1 ("random") is to solving this theoretical situation (given my understanding of striping under lustre).   

	In reality, we have a quite varied workload on our file systems with codes ranging from bio to astrophys and, as such, writes ranging from very small to very large.  Any real-world experience with these situations?  Are there strange inefficiencies or administrative difficulties that should be known previous to enabling "random" offsets?  Any info would be greatly appreciated.
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John White
High Performance Computing Services (HPCS)
(510) 486-7307
One Cyclotron Rd, MS: 50B-3209C
Lawrence Berkeley National Lab
Berkeley, CA 94720