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
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