On Fri, Mar 5, 2010 at 3:12 PM, Jon 'maddog' Hall <mad...@li.org> wrote:
> Bill, > > >ZFS is only on *Solaris and FreeBSD (albeit an old one). Linux > >doesn't yet have a stable, consistent COW filesystem. Certainly a > >combination of the two is a great win. > > It has been some time since I have looked at file systems, and > particularly COW file systems, so pardon me if these questions are > "naive". > COW makes snapshotting easy and can reduce the need for a fsck. NetApp's WAFL is a COW. With WAFL or ZFS, you can have snapshots every 15 minutes and keep multiple copies of the snapshot w/o using significant disk space. BSD (sun's UFS) and LVM allow only 1 snapshot at a time. For backup of a database: freeze the DB, snapshot, start the DB, backup the snapshot, delete the snapshot. Any traction to ext3cow or using the COW layering capability of the UDB > block driver? Or LVM "snapshots"? > > And I can not remember if GFS (Global File System, or even the Google > File System) was COW. > I think GFS is a shared file system. Over iSCSI, Fibre Channel or Infiniband. It can be much faster then NFS and reduces the bottleneck. > Finally, what about the up and coming Btrfs? > >From what I've read it looks like a nimby ZFS with improvements. As has been mentioned, Linux reinvents things instead of building on others sometimes. In this case, because the ZFS license isn't compatible with the GPL in the Linux kernel. And that's a valid reason. OpenSSH was created for similar reasons. btrfs changed the underlying code that should make it much easier to reduce a pool to fewer or smaller disks or increase a RAID5 by adding another disk like some RAID cards allow. Some of the ZFS discussions assume that people will just build another pool and only home user types would do this. It's kindof like seening 2 mice; one is a marsupial and one is a mammal. They're built very differently but function similarly. I'm hoping btrfs takes off and becomes part of Linux as a viable ZFS alternative. ReiserFS is a good example. The transition from 3 to 4 hurt its inclusion in the kernel. Does SuSE still use it as the default FS? Are people still using it? There are lots of projects on filesystems these days. SSDs, Embedded systems, Distributed nodes, HPC, reliability. It's a good thing.
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