[Xen-users] Really slow disk write on Ubuntu

[rudi <rudolone@xxxxxxxxx>]

Hello,

we have a fresh Ubuntu 2.6.32-22-server install on Xen 3.4.0 and we 
observed really slow disk-write performance. Disk writes are so slow 
that the system is almost unusable.
We ran a the classic dd benchmark a few times and the results are really 
discouraging:
rd@ubuntu:~$ time sh -c "dd if=/dev/zero of=bigfile bs=8k count=1000000 
&& sync"
1000000+0 records in
1000000+0 records out
8192000000 bytes (8.2 GB) copied, 2082.15 s, 3.9 MB/s

root@ubuntu:/home/rd# time sh -c "dd if=/dev/zero of=bigfile bs=8k 
count=1000000 && sync"
1000000+0 records in
1000000+0 records out
8192000000 bytes (8.2 GB) copied, 2352.29 s, 3.5 MB/s

root@ubuntu:/home/rd# time sh -c "dd if=/dev/zero of=bigfile bs=8k 
count=1000000 && sync"
1000000+0 records in
1000000+0 records out
8192000000 bytes (8.2 GB) copied, 2544.19 s, 3.2 MB/s

Then, we ran a postgresql benchmark - pgbench - that submits a few 
transactions against a small database. Simulating 15 clients running 200 
transactions each we obtained this result, in transaction per second:
tps: 1462.109434 (excluding connections establishing)

where a non-virtualized workstation result is something like:

tps: 5.833331 (excluding connections establishing)

Running the dd benchmark against the raw disk we obtain good results 
(120MB/s) and a couple of Windows 2003 server guests hosted by the same 
Xen host seem to run fine (but I have no benchmark fo this).
The disk is a HP ProLiant ML350 G6 Server series,
Ubuntu is fully virtualized, 4 cpu, 4 GB RAM.

Do you have any hint?

Thanks




_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users