What IO performance hit in a guest is reasonable?

MadEgg

New Member
Apr 7, 2014
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At my company we're working with Proxmox VE 1.9 (an upgrade to 2.x or 3.x is planned but not yet feasible).

The host machine has 4 146 GB HDD's in RAID-5. Performance, according to "hdparm -Tt /dev/cciss/c0d0" is 5985.53 MB/sec cached and 184.95 MB/sec buffered.

In the host machines this is a lot lower. We're using RAW disk images.

In an Archlinux guest (kernel 3.13.7), this is only 5803.50 MB/sec cached and 59.92 MB/sec buffered (according to hdparm -Tt /dev/vda).

In an Debian Wheezy guest running on the same machine, this is significantly higher at 6620.31 MB/sec cached and 98.40 MB/sec buffered.

Still, it's a performance hit of 50% between the host and the guest. Is this normal / expected? If not, any ideas what could cause this?

Also, any ideas what could cause the huge performance difference between the Archlinux guest and the Debian guest?
 

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