Hi
After some investigations, I found a way to mitigate two issues I have when
working with ZFS over iSCSI (in my case ZoL / LIO) :
* First, and more important issue is that drive-mirror (with a running
guest) will make the guest FS panic if the source storage is ZFS over iSCSI.
See [ https://bugzilla.proxmox.com/show_bug.cgi?id=2384 |
https://bugzilla.proxmox.com/show_bug.cgi?id=2384 ]
* Second, and minor issue : when resizing a guest live, the guest is not
automatically notified about the new size, we have to rescan the device for the
new size to be seen. See [ https://bugzilla.proxmox.com/show_bug.cgi?id=2335 |
https://bugzilla.proxmox.com/show_bug.cgi?id=2335 ]
After some digging, I found that when using scsi-hd (instead of the default
scsi-generic), everything is working correctly. I understand scsi-generic is
supposed to perform better as it bypass the SCSI emulation layer in qemu. But,
I prefer a fully working and stable setup over a +5% more performant but
without live move storage. (BTW, perf penalty with scsi-hd isn't huge, there
are even some workflow in which it performs better, but I'm still measuring it
right now)
In /usr/share/perl5/PVE/QemuServer.pm scsi-generic is curretly hardcoded for
any iscsi backed device (using libiscsi from qemu).
What would be the best way to handle this ?
For the first issue, I'm not the only impacted, and it seems to exists no
matter what iSCSI target is used (ZoL + LIO, ZoL + SCST, FreeNAS with ctld,
OmniOS with Comstar). Should we set scsi-hd for any ZFS over iSCSI storage ?
Should we add a setting on the storage ? (some uses might prefer the small perf
boost of scsi-generic and are not interested in disk move)
What do you think ?
Cheers,
Daniel
--
[ https://www.firewall-services.com/ ]
Daniel Berteaud
FIREWALL-SERVICES SAS, La sécurité des réseaux
Société de Services en Logiciels Libres
Tél : +33.5 56 64 15 32
Matrix: @dani:fws.fr
[ https://www.firewall-services.com/ | https://www.firewall-services.com ]
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