On Sat, Jun 17, 2017 at 1:25 AM, Markus Stockhausen <stockhausen@collogia.de> wrote:

Hi,

we just set up a new 4.1.2 OVirt cluster. It is a quite normal

HDD/XFS/NFS stack that worked quit well with 4.0 in the past.

Inside the VMs we use XFS too.

To our surprise we observe abysmal high IO during mkfs.xfs

and fstrim inside the VM. A simple example:

Step 1: Create 100G Thin disk

Result 1: Disk occupies ~10M on storage

Step 2: Format disk inside VM with mkfs.xfs

Result 2: Disk occupies 100G on storage

Changing the discard flag on the disk does not have any effect.

Are you sure it's discarding, at all?

1. NFS: only NFSv4.2 supports discard. Is that the case in your setup?

2. What's the value of /sys/block/<disk>/queue/discard_granularity ?

3. Can you share the mkfs.xfs command line?

4. Are you sure it's not a raw-sparse image?

Am I missing something?

Best regards.

Markus

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