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Re: [Xen-users] Really slow disk write on Ubuntu
Why not use paravirtualise?
On 24 May 2010 17:20, rudi <rudolone@xxxxxxxxx> wrote:
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
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