Yes Wido, you are correct. There is a RBD pool in the cluster, but is not currently running with a cache attached. The Pool I’m trying to manage here is only used by Librados to write objects directly to the pool as opposed to any of the other niceties that ceph provides.
Specifically I ran: `ceph osd tier cache-mode <hot-storage> forward` which returned `Error EPERM: 'forward' is not a well-supported cache mode and may corrupt your data. pass --yes-i-really-mean-it to force.` Currently we are running 10.2.5. I suspect that it’s fine in our use case, however given the sparsity of the documentation I didn’t like to assume anything. Regards Stuart > On 10 Jan 2017, at 09:52, Wido den Hollander <w...@42on.com> wrote: > >> >> Op 10 januari 2017 om 9:52 schreef Nick Fisk <n...@fisk.me.uk >> <mailto:n...@fisk.me.uk>>: >> >> >>> -----Original Message----- >>> From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of >>> Wido den Hollander >>> Sent: 10 January 2017 07:54 >>> To: ceph new <ceph-users@lists.ceph.com>; Stuart Harland >>> <s.harl...@livelinktechnology.net> >>> Subject: Re: [ceph-users] Write back cache removal >>> >>> >>>> Op 9 januari 2017 om 13:02 schreef Stuart Harland >>>> <s.harl...@livelinktechnology.net>: >>>> >>>> >>>> Hi, >>>> >>>> We’ve been operating a ceph storage system storing files using librados >>>> (using a replicated pool on rust disks). We implemented a >>> cache over the top of this with SSDs, however we now want to turn this off. >>>> >>>> The documentation suggests setting the cache mode to forward before >>>> draining the pool, however the ceph management >>> controller spits out an error about this saying that it is unsupported and >>> hence dangerous. >>>> >>> >>> What version of Ceph are you running? >>> >>> And can you paste the exact command and the output? >>> >>> Wido >> >> Hi Wido, >> >> I think this has been discussed before and looks like it might be a current >> limitation. Not sure if it's on anybody's radar to fix. >> >> https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html >> <https://www.mail-archive.com/ceph-users@lists.ceph.com/msg24472.html> >> > > Might be, but afaik they are using their own application which writes to > RADOS using librados, not RBD. > > Is that correct Stuart? > > Wido > >> Nick >> >>> >>>> The thing is I cannot really locate any documentation as to why it’s >>>> considered unsupported and under what conditions it is expected >>> to fail: I have read a passing comment about EC pools having data >>> corruption, but we are using replicated pools. >>>> >>>> Is this something that is safe to do? >>>> >>>> Otherwise I have noted the read proxy mode of cache tiers which is >>>> documented as a mechanism to transition from write back to >>> disabled, however the documentation is even sparser on this than forward >>> mode. Would this be a better approach if there is some >>> unsupported behaviour in the forward mode cache option? >>>> >>>> Any thoughts would be appreciated - we really cannot afford to corrupt the >>>> data, and I really do not want to have to do some >>> manual software based eviction on this data. >>>> >>>> regards >>>> >>>> Stuart >>>> >>>> >>>> − Stuart Harland: >>>> Infrastructure Engineer >>>> Email: s.harl...@livelinktechnology.net >>>> <mailto:s.harl...@livelinktechnology.net> >>>> >>>> >>>> >>>> LiveLink Technology Ltd >>>> McCormack House >>>> 56A East Street >>>> Havant >>>> PO9 1BS >>>> >>>> IMPORTANT: The information transmitted in this e-mail is intended only for >>>> the person or entity to whom it is addressed and may >>> contain confidential and/or privileged information. If you are not the >>> intended recipient of this message, please do not read, copy, use >>> or disclose this communication and notify the sender immediately. Any >>> review, retransmission, dissemination or other use of, or >>> taking any action in reliance upon this information by persons or entities >>> other than the intended recipient is prohibited. Any views or >>> opinions presented in this e-mail are solely those of the author and do not >>> necessarily represent those of LiveLink. This e-mail >>> message has been checked for the presence of computer viruses. However, >>> LiveLink is not able to accept liability for any damage >>> caused by this e-mail. >>>> >>>> >>>> >>>> _______________________________________________ >>>> ceph-users mailing list >>>> ceph-users@lists.ceph.com >>>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >>> _______________________________________________ >>> ceph-users mailing list >>> ceph-users@lists.ceph.com <mailto:ceph-users@lists.ceph.com> >>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >>> <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com>
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