Re: [patch v2 0/6] Add TRIM support for raid linear/0/1/10

[Holger Kiehl]

Hello,

On Tue, 20 Mar 2012, Shaohua Li wrote:

> 2012/3/20 Holger Kiehl <Holger.Kiehl@xxxxxx>:
> > Hello,
> >
> >
> > On Fri, 16 Mar 2012, Shaohua Li wrote:
> >
> > > The patches add TRIM support for raid linear/0/1/10. I'll add TRIM support
> > > for
> > > raid 4/5/6 later. The implementation is pretty straightforward and
> > > self-explained.
> > >
> > > v1->v2:
> > > 1. fixed a checking issue
> > > 2. dropped discard request plug and replace it with no discard merege,
> > > because
> > > current SCSI layer can't handle discard request merge.
> > Have tested TRIM patches on three different systems with the following
> > hardware/ setup:
> >
> >   1) root mounted on a raid1 over two SAS SSD's (200GB) and /home partition
> >      on a raid0 over a fusionio ioDrive Duo. Is very new and seen very
> >      little usage.
> >
> >   2) root and /home mounted on a raid0 over two Intel X25 Postville
> >      (160GB) connected to a Intel P55 Express chipset. Has seen very
> >      heavy usage for approx. 2 years.
> >
> >   3) root and /home mounted on a raid0 over three OCZ-VERTEX2 (120GB)
> >      connected via ICH7 south bridge. Has seen mild usage for approx.
> >      1.5 years.
> >
> > Made the following observations when running my own benchmark which
> > copies around a lot of small files and deletes them. The benchmark on
> > all systems was always run only on the /home partition ie. on a raid0.
> >
> > For system 1) there is hardly any measurable differnce whether discard
> > is enabled or not (~29000 files per second).
> >
> > On system 2) the performance drops from 6500->3700 files per second,
> > but under normal usage one does not notice any difference.
> do you have the blktrace data when the benchmark is running, especially
> when doing file deletion. I'd like to check the latency of discard in this case.
It is uploaded on ftp://ftp.dwd.de/pub/afd/test/trim

> > System 3) has problems during boot, it is so slow that some operations
> > receive a timeout during boot:
> >
> >  udevd[474]: timeout '/sbin/blkid -o udev -p /dev/md0'
> >  udevd[474]: timeout: killing '/sbin/blkid -o udev -p /dev/md0' [866]
> >  systemd[1]: dev-md3.swap activation timed out. Stopping.
> In this one, discard request is slow. And per SATA standard, discard request
> can't be parallel, so only one request one time, which further slows it down.
Ok, so having three disc in a raid 0 is even worth.

> > Even removing discard does not help and the above errors happen during
> > boot and booting takes a long time.
> this doesn't make sense. If you don't mount with discard option, no
> discard request
> is issued.
I read some where that swap uses discard by default and if I remember
correctly it initializes the whole swap area at boot. So doing that
over three disks might explain why I get those timeout error messages
and after boot these commands work without delay.

Regards,
Holger