[dm-devel] getting feedback on dm-cache statistics tool

[John Stoffel]

Ben> I have a git repo containing a tool I wrote to look at dm-cache
Ben> statistics, not the raw counters in "dmsetup status" but derived
Ben> values that are more directly useful to system administrators and
Ben> developers that want to see whether dm-cache is doing what they
Ben> want it to.  https://github.com/bengland2/dmcache-stat

Ben> Any feedback on this?  Anything missing?  I don't mind adding or
Ben> taking pull requests.  If some other tool can provide the same
Ben> functionality within RHEL then I'm happy to use that.

I'm using Debian Jessie on x86_64 running kernel 4.4.0-rc7 (self
compiled) and it's dying with an error:

    > sudo ./dmcache_stat.py 10 0
    volname, size(GiB), policy, mode
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVLvpBly2guNYp3XUqTVCgGCHequQOBEf9" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVkuRxXnQASgLcdsdFmK9OviYa88Q6buOU" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVM32OGu9FYyW2J5u8Q1zSNh826zw6BnFX" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVabjo7c4R5l6twigsqqfc55LVN6XVag4W-cdata" should be man.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVIWMZ8hjG32sj1LIdQja6QWB4OWkUvUCl" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVkOhak3U4uF82eWXH5JY1F3VhHzMHYV8c-cmeta" should be man.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVR1c11WDl2e86Ko9OmuWYRIUNXExHQnX1" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVvdF6NWzpggiPLD202jpru363Z5LfB5Lo" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wV40890zsM04q5zMIs0qdeCDfG9fc9FwbF" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVrdBEgHTcrXLHDWNrbFotKPeLt2TfbRVo" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVi37feovUsvWbysOk8PI2bbdjqokieGx2-cdata" should be man.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVnp1To0klyekIS85gueDeq2EsYg5Osj44" should be mangled b.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVas2sZsZM8mw0VXDgx03ryaq351RUEL4j-cmeta" should be man.
    The UUID "LVM-HWDbRMPFL85!mVbEi4wru5#G7YfWK3wVbbcg3pVFZyDngdRLS4aECbc571Lyb5MI" should be mangled b.
    Command failed
    Traceback (most recent call last):
      File "./dmcache_stat.py", line 198, in <module>
	  s2 = poll_dmcache()
      File "./dmcache_stat.py", line 172, in poll_dmcache
	dmsetup_out = subprocess.check_output(['dmsetup', 'status'])
      File "/usr/lib/python2.7/subprocess.py", line 573, in check_output
	raise CalledProcessError(retcode, cmd, output=output)
      subprocess.CalledProcessError: Command '['dmsetup', 'status']' returned non-zero exit status 1


But this is partly because my UUIDs aren't being handled properly and I've been loathe to follow the process for rebuilding them because I'm scared.  And it's my main fileserver.  Maybe this weekend if I have time.


The other comment is that the usage should be more like:

    dmcache-stat <interval> [<count>]

where if you don't provide the count, it defaults to going forever, like iostat/vmstat, etc.

And now that I think of it, I'm using lvmcache, not dmcache or bcache...

> sudo lvs
  LV           VG     Attr       LSize   Pool         Origin        Data%  Meta%  Move Log Cpy%Synct
    backups      bacula -wi-ao----   2.73t
    incrs        bacula -wi-ao----   2.64t
    drupal       data   -wi-ao----  50.00g
    home         data   Cwi-aoC--- 550.00g homecacheLV  [home_corig]
    homecacheLV  data   Cwi---C---  50.00g
    local        data   Cwi-aoC--- 335.00g localcacheLV [local_corig]
    localcacheLV data   Cwi---C---  50.00g
    minecraft    data   -wc-ao----  20.00g
    nas          data   -wi-ao---- 600.00g
    pete         data   -wi-a----- 800.00g
    vm1          data   -wc-ao----  20.00g
    winxp        data   -wi-a----- 170.00g
    root         quad   -wi-ao----  37.25g
    swap_1       quad   -wi-ao----   7.45g
    var          quad   -wi-ao----  58.62g

Though looking at this list, I really should just nuke that ancient WinXP VM image I have.  LOL.