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Re: [linux-lvm] Allocation Policy for Cloud Computing needed



Sebastian Riemer wrote:
Hi LVM list,

I'm experimenting with storage for many QEMU/KVM virtual machines in
cloud computing. I've got many concurrent IO processes and 24 hard
drives. I've tested the scalability with a single IO reader process per
hard drive. Single drives scale best and have the best performance of
cause, but we need mirroring and volume management. So I've created MD
RAID-1 arrays and created on each a VG and two LVs. This gives me good
overall performance (up to 2 GB/s, HBA limit: 2.2 GB/s).

Then, I've tested to put all my RAID-1 arrays into a single VG, because
LV size should be adjustable over all hard drives. I've tried all
allocation policies but none does what I want to achieve here. Yeah,
that this isn't implemented fully is in the man page, ... .

I want to have an allocation which distributes the LVs equally over the
PVs as long as space is left and LVs aren't resized. The goal is to
minimize the number of concurrent IO processes per hard drive (striping
is total crap in this situation).

I've tested LVM2 2.02.66 and kernel 3.0.15. Is something like that
implemented in newer releases or is something like that intended to be
implemented in near future? Or does someone want to implement this
together with me?

Thanks, cheers,

Sebastian

I wrote a script to do this, with LVM 1 that just extended the lv in chunks over a range of PVs until it was full. while it worked on LVM it produced lots of backups in /etc. I felt with the LVM stripe function that this was not necessary, and could acheive the same thing by using large stripe size, as LVM allows concats of different stripeness it was not a problem extending the lv.

James.


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