[Linux-cluster] caching of san devices....

Alan Brown ajb2 at mssl.ucl.ac.uk
Tue Apr 3 13:14:09 UTC 2012

Real Dumb Question[tm] time....

Has anyone tried putting bcache/flashcache in front of shared storage in 
a GFS2 cluster (on each node, of course)

Did it work?

Should it work?

Is it safe?

Are there ways of making it safe?

Am I mad for thinking about it?


Spinning disks are slow to seek, large arrays even more so.

As soon as there's a significant load on our GFS2 cluster the random io 
limitations of the SAN hardware become the single most important factor 
limiting performance.

Only "so much" ram can be installed in any hardware to increase page and 
dentry caching before physical limits are hit.

SSD SAN arrays are hideously expensive and can't always be justified to 
"the powers that be".

Universities are always tightly funded, but there are many other 
entities facing similar problems.

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