WARNING: Pool zeroing and 1.00 MiB large chunk size slows down thin provisioning?

Yakooza · 09-09-2018, 08:08 PM

Hi Guys,

I am creating a KVM on CentOS 7.x with Thin provisioning and when I create the thin provisioning inside LVM I get this warning. Could you please help me if you know how can fix this issue? Or is it an issue? I do not want a slow performance. Just to make sure

Code:

# lvcreate --size 1.83TiB --type thin-pool --thinpool thin-vps vps
  Rounding up size to full physical extent 1.83 TiB
  Thin pool volume with chunk size 1.00 MiB can address at most 253.00 TiB of data.
  WARNING: Pool zeroing and 1.00 MiB large chunk size slows down thin provisioning.
  WARNING: Consider disabling zeroing (-Zn) or using smaller chunk size (<512.00 KiB).
  Logical volume "thin-vps" created.
[root@tx01 ~]# lvs
  LV       VG  Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  thin-vps vps twi-a-tz-- 1.83t             0.00   0.39

Thank you

berndbausch · 09-09-2018, 10:38 PM

Code:

# lvcreate --size 1.83TiB --type thin-pool --thinpool thin-vps vps
  Rounding up size to full physical extent 1.83 TiB
  Thin pool volume with chunk size 1.00 MiB can address at most 253.00 TiB of data.
  WARNING: Pool zeroing and 1.00 MiB large chunk size slows down thin provisioning.
  WARNING: Consider disabling zeroing (-Zn) or using smaller chunk size (<512.00 KiB).
  Logical volume "thin-vps" created.
[root@tx01 ~]# lvs
  LV       VG  Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  thin-vps vps twi-a-tz-- 1.83t             0.00   0.39

From the lvmthin man page:

Quote:

When a thin pool provisions a new data block for a thin LV, the new block is first overwritten with zeros.

The size of the data block is given by the chunk size, which you can control with -c. I guess zeroing a 1MB chunk can take a few fractions of a second, but it probably doesn't matter as long you don't create thinly provisioned volumes at a high rate.

Yakooza · 09-10-2018, 04:00 AM

Quote:

Originally Posted by berndbausch

Code:

# lvcreate --size 1.83TiB --type thin-pool --thinpool thin-vps vps
  Rounding up size to full physical extent 1.83 TiB
  Thin pool volume with chunk size 1.00 MiB can address at most 253.00 TiB of data.
  WARNING: Pool zeroing and 1.00 MiB large chunk size slows down thin provisioning.
  WARNING: Consider disabling zeroing (-Zn) or using smaller chunk size (<512.00 KiB).
  Logical volume "thin-vps" created.
[root@tx01 ~]# lvs
  LV       VG  Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  thin-vps vps twi-a-tz-- 1.83t             0.00   0.39

From the lvmthin man page:

The size of the data block is given by the chunk size, which you can control with -c. I guess zeroing a 1MB chunk can take a few fractions of a second, but it probably doesn't matter as long you don't create thinly provisioned volumes at a high rate.

Thank you for your answer. Noted