From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomasz Chmielewski Subject: LVM vs btrfs as a "volume manager" for SANs Date: Wed, 22 Apr 2009 21:20:23 +0200 Message-ID: <49EF6DF7.9020406@wpkg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed To: linux-btrfs@vger.kernel.org Return-path: List-ID: Right now, the majority of Linux users probably have LVM on their SAN devices (i.e those being iSCSI targets). Using LVM on a SAN device is easy: just create a new logical volume or its snapshot, make it a target to iSCSI initiators, done. I was wondering how btrfs would fit here and if it could replace LVM. I see the following benefits of using btrfs instead of LVM: - you can create sparse files which would grow as iSCSI initators use more space (you can do it with ext3 now as well) - you can use btrfs compression, to further reduce used space and perhaps increase speed (SANs are mostly IO bound, not CPU bound) - LVM has a big performance hit when using snapshots; btrfs doesn't However, with btrfs, I'm not sure about: - what happens if SAN machine crashes while the iSCSI file images were being written to; with LVM and its block devices, I'm somehow more confident it wouldn't make more data loss than necessary - taking snapshots of individual files (file images on SAN) is not possible with btrfs? Probably they would have to be placed in separate directories first to make snapshots - some minor manageability issue -- Tomasz Chmielewski http://wpkg.org