-- Don Granaman <[EMAIL PROTECTED]>
> It isn't mount points that matter for I/O contention, it is spindles and
> channels - the physical disk layout. If this is one set of disks used in
> one large RAID-5 setup, then creating multiple mount points for logical
> volumes created on top of it will do nothing to reduce I/O contention.
> To balance out I/O, you MUST know the physical layout underneath the
> logical volumes and balance the I/O against that.
Actually, you can help balance things a bit with careful LVM management.
There is caching and I/O optimization going on at that level also. For
example, you may have two RAID5 stripes (PV's) combined into the same
volume (VG). By specifying which of the PV's your LV's are created/
extended onto you can at least partially balance the load. There is
obviously no benefit to multiple mounts for a single LV, but you can get
some improvement by creating multiple LV's within the VG (which then
do require separate mount points unless you're using raw I/O).
You can do some of this without even knowing the physical layout of the
spindles -- though that obviously helps. Knowing which PV's (e.g.,
RAID5 groupings or mirror sets) are aviailable goes a long way to
balancing the load.
Main problem I've found is the absolute lack of shell tools for looking
at how the I/O load maps at the spindle level. At that point all you
have are the PV's reported by iostat & friends. Unless you know how the
LV's were laid out it leaves you with little idea as to how the filesystem
maps onto the load.
--
Steven Lembark 2930 W. Palmer
Workhorse Computing Chicago, IL 60647
+1 800 762 1582
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Author: Steven Lembark
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