That would be the case for me. I think all data during one day would fit into the cache, and we could slowly flush back over night (or even over the weekend). But my impression is, I would have to test it. So my initial question: Do I have to stop all VMs before activating the cache? And restart one by one with the cache enabled? -- ----------------------------------------------------------------- Robert Eikermann M.Sc.RWTH | Software Engineering Lehrstuhl für Software Engineering | RWTH Aachen University Ahornstr. 55, 52074 Aachen, Germany | http://www.se-rwth.de Phone ++49 241 80-21306 / Fax -22218 | -----Ursprüngliche Nachricht----- Von: Fyodor Ustinov [mailto:ufm@xxxxxx] Gesendet: Montag, 16. September 2019 13:00 An: Wido den Hollander <wido@xxxxxxxx> Cc: Eikermann, Robert <eikermann@xxxxxxxxxx>; ceph-users@xxxxxxx Betreff: Re: Re: Activate Cache Tier on Running Pools Hi! Cache tiering is a great solution if the cache size is larger than the hot data. Even better if the data can cool quietly in the cache. Otherwise, it’s really better not to do this. ----- Original Message ----- > From: "Wido den Hollander" <wido@xxxxxxxx> > To: "Eikermann, Robert" <eikermann@xxxxxxxxxx>, ceph-users@xxxxxxx > Sent: Monday, 16 September, 2019 12:51:45 > Subject: Re: Activate Cache Tier on Running Pools > On 9/16/19 11:36 AM, Eikermann, Robert wrote: > > > > > > Hi, > > > > I’m using Ceph in combination with Openstack. For the “VMs” Pool I’d > like to enable writeback caching tier, like described here: [ > https://docs.ceph.com/docs/luminous/rados/operations/cache-tiering/ | > https://docs.ceph.com/docs/luminous/rados/operations/cache-tiering/ ] . > > > > > Can you explain why? The cache tiering has some serious flaws and can > even decrease performance instead of improve it. > > What are you trying to solve? > > Wido > > > > > Should it be possible to do that on a running pool? I tried to do so > and immediately all VMs (Linux Ubuntu OS) running on Ceph disks got > readonly filesystems. No errors were shown in ceph (but also no > traffic arrived after enabling the cache tier). Removing the cache > tier , rebooting the VMs and doing a filesystemcheck repaired everything. > > > > Best > > Robert > > > > _______________________________________________ > ceph-users mailing list -- [ mailto:ceph-users@xxxxxxx | > ceph-users@xxxxxxx ] To unsubscribe send an email to [ > mailto:ceph-users-leave@xxxxxxx | ceph-users-leave@xxxxxxx ] > > _______________________________________________ > ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an > email to ceph-users-leave@xxxxxxx _______________________________________________ ceph-users mailing list -- ceph-users@xxxxxxx To unsubscribe send an email to ceph-users-leave@xxxxxxx
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