From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul B. Henson Date: Wed, 5 Feb 2014 12:12:06 -0800 Subject: cache support In-Reply-To: <52F1E9DC.60809@mglug.de> References: <096101cf2214$d241ed60$76c5c820$@acm.org> <52F1E9DC.60809@mglug.de> Message-ID: <0a3601cf22ae$8cdd4900$a697db00$@acm.org> List-Id: To: lvm-devel@redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit > From: Oliver Rath > Sent: Tuesday, February 04, 2014 11:36 PM > > you can create a cache-device with dm-cache, i.e. /dev/mapper/cache0, > which consists your underlying disks cached by your ssd. I investigated that, although I never prototyped it. Using dm-cache directly involves size calculations and an annoying number of messy manual operations, I was hoping lvm would hide most of that from the user level and make it easier to do :). > cache0, getting the right name for this. As result you get the disk ids > twice, so you have to filter the ids by lvm.conf. > > @list: Is there a solution for this "doubling" case? I've deployed lvm on mdraid in the past, specifically on mirrors using the older metadata format such that each half of the mirror appears to be a pv on its own. I never fiddled with filters, but somehow lvm figured out that it should use the /dev/md device for the pv and not the raw /dev/sd components. > Alternativly you can use bcache, which needs a "superblock" on both I looked at bcache, which is relatively easy to use and does match my use case. However, after hanging out on the mailing list for a while, the developers didn't seem to reliably respond to postings of crashes or data corruption or other issues, which made me somewhat leery of deployment in production. On the device mapper mailing list, the developers seem to respond to pretty much every question or problem report about dm-cache, which gives one a little bit more of a warm fuzzy ;). > enhanceIO (not in standard kernel yet), which caches your device I took a look at that too, but I'd really prefer something in the mainline kernel for production deployment. Thanks much.