From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nikolaus Rath Subject: Re: bcache and LVM Date: Mon, 08 Feb 2016 14:02:52 -0800 Message-ID: <87r3gmrhbn.fsf@thinkpad.rath.org> References: <87k2mgo2rz.fsf@vostro.rath.org> <20160208144419.Horde.Ci1_2KcBCEnOa-WxsDN90oU@www3.nde.ag> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from plane.gmane.org ([80.91.229.3]:51072 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753464AbcBHWIO (ORCPT ); Mon, 8 Feb 2016 17:08:14 -0500 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1aStyc-0005LV-9t for linux-bcache@vger.kernel.org; Mon, 08 Feb 2016 23:08:10 +0100 Received: from ebox.rath.org ([45.79.69.51]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 08 Feb 2016 23:08:10 +0100 Received: from Nikolaus by ebox.rath.org with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 08 Feb 2016 23:08:10 +0100 Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: linux-bcache@vger.kernel.org On Feb 08 2016, "Jens-U. Mozdzen" wrote: > Hi Nikolaus, > > Zitat von Nikolaus Rath : >> Hello, >> >> The internet claims that using bcache with LVM is not a good idea >> (eg. on https://wiki.archlinux.org/index.php/Bcache )- but I wasn't = able >> to find any substantial information other than this general >> recommendation. > > looking at that article, it only references possibly ill-handled > "discard" operations, when running bcache on top of LVM. Well, it says: | Warning: |=20 | it is widely recommended to use Bcache underneath any other block | layer. To me this implies that running it on top of another block layer is dangerous (why warn about it otherwise?).=20 > The article itself does positively mention sub-dividing bcache device= s > using LVM. Yep, but the talk page then says: | Initially, LVM did not recognize my /dev/bcache0 when I wanted to | create a physical volume on it. For anyone else who has that issue, | this may be relevant: | http://www.redhat.com/archives/linux-lvm/2012-March/msg00005.html. >> Is this still (or has ever been) correct? If so, what issues can ari= se? >> And does this happen only when using bcache on top of an LVM LV, or = also >> when using a bcache device as an LVM PV? > > We're running bcache between MD-RAID (RAID6 for the HDD backing store > and RAID1 for caching SSDs) and LVM2 (using bcache0 as the only PV fo= r > the volume group) without any noticeable problem, for moderate to > significant load (SAN/NAS servers with NFS, Samba, and virtual > machines' storage via SCST/FC and SCST/iSCSI). Thanks for the datapoint! What kernel version do you use? Best, -Nikolaus --=20 GPG encrypted emails preferred. Key id: 0xD113FCAC3C4E599F =46ingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F =C2=BBTime flies like an arrow, fruit flies like a Banana.= =C2=AB