Subject: Re: [vserver] Hard time with IO bottleneck
From: Herbert Poetzl <herbert@13thfloor.at>
Date: Fri, 22 Aug 2008 18:33:23 +0200

On Tue, Jun 24, 2008 at 11:24:59AM +0200, Markus Fischer wrote:
> I guess it makes not much sense without some numbers/versions:
> 
> Kernel 2.6.22.19 with vserver 2.2.0.7, using two 250GB disc in
> mirroring RAID and on top of that LVM.

| I'm having a hard time with my system when it comes to IO performance.

| As an example, I've three directories to delete with about 50000 files
| in each. I'm deleting on the "host" system already, using "ionice -c3"
| (only when idle) and CFQ scheduler is activated.

the bottleneck with disk I/O is mostly caused
by seeking (which is very slow compared to 
throughput), so maybe your raid/filesystem/disk
combination is very unfortunate, and any kind
of extensive seeking causes the I/O subsystem
to congest

| While this is done, I've about 11 vserver running.

what do they do? disk seeks too? ideling?

| As long as I have the delete job *not* running, the system has a load
| As < 1.0. soon as I start/resume the job, in short the load goes over
| As e.g. 12 !

a load of 12 is nothing bad per se, it just
means that 12 more processes could be run
but need to wait on some I/O or CPU

| I'm currently completely puzzled as to what is going on here. Using
| vtop I can't find any two processes on top being the cause for the
| load. The list usually looks like

first, check with iostat and vmstat to get
an idea about the ongoing I/O 

the next step would be to recreate the guest
I/O in some way, so that you can run it on the
host (without hurting anything). this can then
be used to check without the Linux-VServer patch
(to verify if that is some kind of mainline
issue/regression)

HTH,
Herbert


> thanks,
> - Markus