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

[Holger Kiehl]

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.

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.

Even removing discard does not help and the above errors happen during
boot and booting takes a long time.

The performance in the benchmark drops from 4000->600 files per second.

Regards,
Holger
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