Re: Issue with fstrim and Nova hw_disk_discard=unmap

[Fulvio Galeazzi <fulvio.galeazzi@xxxxxxx>]

Hallo Jason,
    thanks for your feedback!

-------- Original Message -------->>   * decorated a CentOS image with 
hw_scsi_model=virtio--scsi,hw_disk_bus=scsi> > Is that just a typo for 
"hw_scsi_model"?
Yes, it was a typo when I wrote my message. The image has virtio-scsi as 
it should.

> > I see that commands:
> > rbd --cluster cephpa1 diff cinder-ceph/${theVol} | awk '{ SUM += $2 } END {
> > print SUM/1024/1024 " MB" }' ; rados --cluster cephpa1 -p cinder-ceph ls |
> > grep rbd_data.{whatever} | wc -l
>
> That's pretty old-school -- you can just use 'rbd du" now to calculate
> the disk usage.

Good to know, thanks!

> >   show the size increases but does not decrease when I execute delete the
> > temporary file and execute
> >          sudo fstrim -v /
>
> Have you verified that your VM is indeed using virtio-scsi? Does
> blktrace show SCSI UNMAP operations being issued to the block device
> when you execute "fstrim"?

Thanks for the tip, I think I need some more help, please.

Disk on my VM is indeed /dev/sda rather than /dev/vda. The XML shows:
.....
    <disk type='network' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
.....
      <source protocol='rbd' 
name='cinder-ceph/volume-80838a69-e544-47eb-b981-a4786be89736'>
.....
      <target dev='vda' bus='scsi'/>
      <serial>80838a69-e544-47eb-b981-a4786be89736</serial>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <controller type='scsi' index='0' model='virtio-scsi'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' 
function='0x0'/>
    </controller>


As for blktrace, blkparse shows me tons of lines, please find below the 
first ones and one of the many group of lines which I see:

  8,0    0       11     4.333917112 24677  Q FWFSM 8406583 + 4 [fstrim]
  8,0    0       12     4.333919649 24677  G FWFSM 8406583 + 4 [fstrim]
  8,0    0       13     4.333920695 24677  P   N [fstrim]
  8,0    0       14     4.333922965 24677  I FWFSM 8406583 + 4 [fstrim]
  8,0    0       15     4.333924575 24677  U   N [fstrim] 1
  8,0    0       20     4.340140041 24677  Q   D 986016 + 2097152 [fstrim]
  8,0    0       21     4.340144908 24677  G   D 986016 + 2097152 [fstrim]
  8,0    0       22     4.340145561 24677  P   N [fstrim]
  8,0    0       24     4.340147495 24677  Q   D 3083168 + 1112672 [fstrim]
  8,0    0       25     4.340149772 24677  G   D 3083168 + 1112672 [fstrim]
.....
  8,0    0       50     4.340556955 24677  Q   D 665880 + 20008 [fstrim]
  8,0    0       51     4.340558481 24677  G   D 665880 + 20008 [fstrim]
  8,0    0       52     4.340558728 24677  P   N [fstrim]
  8,0    0       53     4.340559725 24677  I   D 665880 + 20008 [fstrim]
  8,0    0       54     4.340560292 24677  U   N [fstrim] 1
  8,0    0       55     4.340560801 24677  D   D 665880 + 20008 [fstrim]
.....

Apologies for my ignorance, is the above enough to understand whether 
SCSI UNMAP operations are being issued?

  Thanks a lot!

			Fulvio

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