[PVE-User] Risks for using writeback on Ceph RBD

[Mark Schouten]

Hi,

We've noticed some performance wins on using writeback for Ceph RBD
devices, but I'm wondering how we should project risks on using
writeback. Writeback isn't very unsafe, but what are the risks in case
of powerloss of a host?

Thanks,

[Alexandre DERUMIER]

Like all writeback, you'll lost datas in memory before the fsync of the filesystem, but not corruption of the filesystem. (writeback = rbd_cache=true)

note that rbd writeback help only for sequential of small writes (aggregate in 1big transaction to send to ceph).

Also, read latency is bigger when writeback is enable.

----- Mail original -----
De: "Mark Schouten" <***@tuxis.nl>
À: "proxmoxve" <pve-***@pve.proxmox.com>
Envoyé: Lundi 12 Novembre 2018 14:45:41
Objet: [PVE-User] Risks for using writeback on Ceph RBD

Hi,

We've noticed some performance wins on using writeback for Ceph RBD
devices, but I'm wondering how we should project risks on using
writeback. Writeback isn't very unsafe, but what are the risks in case
of powerloss of a host?

Thanks,
--
Mark Schouten | Tuxis Internet Engineering
KvK: 61527076 | http://www.tuxis.nl/
T: 0318 200208 | ***@tuxis.nl


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