[ovirt-users] OVirt 4.1.2 - trim/discard on HDD/XFS/NFS contraproductive

[Yaniv Kaul]

On Sat, Jun 17, 2017 at 1:25 AM, Markus Stockhausen <stockhausen at 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?
Y.


> Am I missing something?
>
> Best regards.
>
> Markus
>
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