LVM striping on luns
Le 26/01/2012 18:26, Matty Sarro a écrit :
I am working with a number of boxes right now. Each one has several LUN's
from a SAN attached via fibre channel. The arrays on the SAN should all be
raid 10. Now, what I'm curious about is if I will get any performance boost
at all from using striping on the logical volumes, or if I should just use
linear volumes? It seems like writing across each lun with striping makes
sense, but at the same time it'd be extra CPU load.
Any advice would greatly be appreciated. Thanks!
In a SAN environment you have to consider that one LUN on a RAID can
influence the performance of the others LUNs on the same RAID as far as
they share the same disks.
So, on a RAID, if you have two LUNs, "A" being part of a stripped
filesystem, "B" being independent, if "B" becomes intensively used, it
will also decrease the performance of "A".
On a stripped filesystem, reads and writes occur on all the Physical
Volumes of the pool, if one of them ("A" in my example) becomes slow,
the performance of the whole filesystem will also becomes slow.
Log story short : a single independent LUN can decrease the performance
of a stripped filesystem.
If you use "linear", you might not really use all the throughput of the
LUNs at first because your data won't be spread on all of them but if
one raid becomes intensively used (by a LUN independent of your LVM
setup) it won't impact the filesystem as much as with stripping.
I hope this helps,
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