[PVE-User] ZFS Disk Usage unexpected high

[PVE-User] ZFS Disk Usage unexpected high

[Konold, Martin]

Hi,

I set up a single VM which currently used 15TB of data.
/dev/sdb is technically a ZFS volume on the Proxmox Host.

[root@vm ~]# df -h /data
Filesystem      Size  Used Avail Use% Mounted on
/dev/sdb         40T   15T   25T  37% /data
[root@vm ~]# du -s /data/
14874345100     /data/

[root@host /]# zfs list zfs01/PVE-BE/vm-1-disk-1
NAME                         USED  AVAIL     REFER  MOUNTPOINT
zfs01/PVE-BE/vm-1-disk-1  31.5T  5.82T     31.5T  -

Why is the usage on the host about twice as large as within the vm?
(Yes, I have given fstrim and discard a try).

-- 
Regards
ppa. Martin Konold

--
Martin Konold - Prokurist, CTO
KONSEC GmbH -⁠ make things real
Amtsgericht Stuttgart, HRB 23690
Geschäftsführer: Andreas Mack
Im Köller 3, 70794 Filderstadt, Germany

Re: [PVE-User] ZFS Disk Usage unexpected high

[Yanni M.]

This is a common issue on raidz based pools. Assuming 4k sectors
(ashift=12) and zvol with 8K volblocksize, each 8K (2-sector) block uses a
single sector (4k) of parity. So 15TB of 8KB blocks (default
volblocksize=8k) takes up at least 22.5TB space on disk (including parity).
You will use less parity by increasing the volblock size (e.g.
volblocksize=32k, or the default recordsize=128k for filesystems) in
exchange of a possible lower performance. Another solution would be using a
pool of striped mirrors (RAID10). This problem does not exist in such pools
(as there are no parity blocks used).




On Mon, 5 Apr 2021 at 09:23, Konold, Martin <martin.konold@konsec.com>
wrote:

>
> Hi,
>
> I set up a single VM which currently used 15TB of data.
> /dev/sdb is technically a ZFS volume on the Proxmox Host.
>
> [root@vm ~]# df -h /data
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdb         40T   15T   25T  37% /data
> [root@vm ~]# du -s /data/
> 14874345100     /data/
>
> [root@host /]# zfs list zfs01/PVE-BE/vm-1-disk-1
> NAME                         USED  AVAIL     REFER  MOUNTPOINT
> zfs01/PVE-BE/vm-1-disk-1  31.5T  5.82T     31.5T  -
>
> Why is the usage on the host about twice as large as within the vm?
> (Yes, I have given fstrim and discard a try).
>
> --
> Regards
> ppa. Martin Konold
>
> --
> Martin Konold - Prokurist, CTO
> KONSEC GmbH -⁠ make things real
> Amtsgericht Stuttgart, HRB 23690
> Geschäftsführer: Andreas Mack
> Im Köller 3, 70794 Filderstadt, Germany
> <https://www.google.com/maps/search/Im+K%C3%B6ller+3,+70794+Filderstadt,+Germany?entry=gmail&source=g>
>
> _______________________________________________
> pve-user mailing list
> pve-user@lists.proxmox.com
> https://lists.proxmox.com/cgi-bin/mailman/listinfo/pve-user
>

Re: [PVE-User] ZFS Disk Usage unexpected high

[Maximilian Hill]

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Hi,

I got the same issue with different RAID-Z setups lately.

We worked around it, but I don't want to go into detail abaout that
before I know. why that happened.


Regards
Maximilian Hill

On Mon, Apr 05, 2021 at 10:22:56AM +0200, Konold, Martin wrote:
> 
> Hi,
> 
> I set up a single VM which currently used 15TB of data.
> /dev/sdb is technically a ZFS volume on the Proxmox Host.
> 
> [root@vm ~]# df -h /data
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/sdb         40T   15T   25T  37% /data
> [root@vm ~]# du -s /data/
> 14874345100     /data/
> 
> [root@host /]# zfs list zfs01/PVE-BE/vm-1-disk-1
> NAME                         USED  AVAIL     REFER  MOUNTPOINT
> zfs01/PVE-BE/vm-1-disk-1  31.5T  5.82T     31.5T  -
> 
> Why is the usage on the host about twice as large as within the vm?
> (Yes, I have given fstrim and discard a try).
> 
> -- 
> Regards
> ppa. Martin Konold

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