On Mon, Jul 12, 2010 at 05:13:16PM -0500, Stan Hoeppner wrote: > Arcady Genkin put forth on 7/12/2010 11:52 AM: > > On Mon, Jul 12, 2010 at 02:05, Stan Hoeppner <[email protected]> wrote: > > > >> lvcreate -i 10 -I [stripe_size] -l 102389 vg0 > >> > >> I believe you're losing 10x performance because you have a 10 "disk" mdadm > >> stripe but you didn't inform lvcreate about this fact. > > > > Hi, Stan: > > > > I believe that the -i and -I options are for using *LVM* to do the > > striping, am I wrong? > > If this were the case, lvcreate would require the set of physical or pseudo > (mdadm) device IDs to stripe across wouldn't it? There are no options in > lvcreate to specify physical or pseudo devices. The only input to lvcreate is > a volume group ID. Therefor, lvcreate is ignorant of the physical devices > underlying it, is it not?
Have a closer look at lvcreate(8). The last arguments are:
[-Z|--zero y|n] VolumeGroupName [PhysicalVolumePath[:PE[-PE]]...]
So after the VG, you can specify explicitly the exact PEs within
that VG to stripe across that the -I/-i options configure.
I'm unsure why one would necessarily /want/ to do that. I run LVM
on top of md RAID1. Here, I have a single PV on top of the RAID
array, and I can't see that adding additional striping on top of
that would benefit performance in any way. I can only assume it
makes sense if you /don't/ have underlying RAID and want to tell
LVM to stripe over multiple PVs on different physical discs,
which /would/ have some performance impact since you spread the
I/O over multiple discs.
AFAICT the striping options are entirely pointless when layered on
RAID, and could be responsible for the performance issues if it
can have a negative impact (such as thrashing the disks if you
tell it to write multiple stripes to a single disc).
Regards,
Roger
--
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