Here are some recent benchmarks on bcache in Linux kernel 4.1 http://www.phoronix.com/scan.php?page=article&item=linux-41-bcache&num=1 On Fri, 26 Jun 2015 at 11:12, Nick Fisk <n...@fisk.me.uk> wrote:
> I think flashcache bombs out, I must admit I have tested that yet, but as > I would only be running it in writecache mode, there is no requirement I > can think of for it to keep on running gracefully. > > > > *From:* ceph-users [mailto:ceph-users-boun...@lists.ceph.com] *On Behalf > Of *Dominik Zalewski > *Sent:* 26 June 2015 10:54 > *To:* Nick Fisk > *Cc:* ceph-users@lists.ceph.com > *Subject:* Re: [ceph-users] Ceph and EnhanceIO cache > > > > Thanks for your reply. > > > > Do you know by any chance how flashcache handles SSD going offline? > > > > Here is an snip from enhanceio wiki page: > > > > Failure of an SSD device in read-only and write-through modes is > > handled gracefully by allowing I/O to continue to/from the > > source volume. An application may notice a drop in performance > but it > > will not receive any I/O errors. > > > > Failure of an SSD device in write-back mode obviously results > in the > > loss of dirty blocks in the cache. To guard against this data > loss, two > > SSD devices can be mirrored via RAID 1. > > > > EnhanceIO identifies device failures based on error codes. > Depending on > > whether the failure is likely to be intermittent or permanent, > it takes > > the best suited action. > > > > Looking at mailing list and github commits, both flashcache and enhanceio had > not much going on since last year. > > > > Dominik > > > > On Fri, Jun 26, 2015 at 10:28 AM, Nick Fisk <n...@fisk.me.uk> wrote: > > > -----Original Message----- > > From: ceph-users [mailto:ceph-users-boun...@lists.ceph.com] On Behalf Of > > Dominik Zalewski > > Sent: 26 June 2015 09:59 > > To: ceph-users@lists.ceph.com > > Subject: [ceph-users] Ceph and EnhanceIO cache > > > > Hi, > > > > I came across this blog post mentioning using EnhanceIO (fork of > flashcache) > > as cache for OSDs. > > > > > > http://xo4t.mj.am/link/xo4t/jgu89z1/1/cdr6ly7c3QuQHguxILKOvQ/aHR0cDovL3d3dy5zZWJhc3RpZW4taGFuLmZyL2Jsb2cvMjAxNC8xMC8wNi9jZXBoLWFuZC1lbmhhbmNlaW8v > > > > > http://xo4t.mj.am/link/xo4t/jgu89z1/2/jneqhzCbW8BNS2K_vOBBVw/aHR0cHM6Ly9naXRodWIuY29tL3N0ZWMtaW5jL0VuaGFuY2VJTw > > > > > > I'm planning to test it with 5x 1TB HGST Travelstar 7k1000 2.5inch OSDs > and > > using 256GB Transcend SSD as enhanceio cache. > > > > I'm wondering if anyone is using EnhanceIO or others like bcache, > dm-cache > > with Ceph in production and what is your experience/results. > > Not using in production, but have been testing all of the above both > caching the OSD and RBD's. > > If your RBD's are being used in scenarios where small sync writes are > important (iscsi,database's) then caching the RBD's is almost essential. My > findings:- > > FlashCache - Probably the best of the bunch. Has sequential override and > hopefully facebook will continue to maintain it > EnhanceIO - Nice that you can hot add the cache, but is likely to no > longer be maintained, so risky for production > DMCache - Well maintained, but biggest problem is that it only caches > writes for blocks that are already in cache > Bcache - Didn't really spend much time looking at this. Looks as if > development activity is dying down and potential stability issues > DM-WriteBoost - Great performance, really suits RBD requirements. > Unfortunately the ram buffering part seems to not play safe with iSCSI use. > > With something like flashcache on a RBD I can max out the SSD with small > sequential write IO's and it then passes them to the RBD in nice large > IO's. Bursty random writes also benefit. > > Caching the OSD's, or more specifically a small section where the levelDB > lives can greatly improve small block write performance. Flashcache is best > for this as you can limit the sequential cutoff to the levelDB transaction > size. DMcache is potentially an option as well. You can probably halve OSD > latency by doing this. > > > > > Thanks > > > > Dominik > > > > > >
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