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The Next3 filesystem

The Next3 filesystem

Posted May 13, 2010 9:03 UTC (Thu) by ringerc (subscriber, #3071)
Parent article: The Next3 filesystem

NTFS snapshots (volume shadow copies) are the one thing I really miss as a Linux server admin. LVM snapshots do *not* cut it for all purposes:

- They require LVM, which has its own issues and isn't always desirable

- They require storage to be reserved for them and allocated to them in advance

- They don't gracefully age out and aren't quietly removed when they run out of backing store. In fact, I recently had a server fail to boot because of an LVM snapshot that'd filled up.

- They need the file system to be capable of being mounted read-only from a dirty state. Not all file systems can handle this.

I find LVM snapshots to be well suited to taking backups, where I need to snapshot a volume, read the snapshot contents, unmount the snapshot and destroy it.

I find them rather less than ideal for when I just want to keep a few snapshots around to provide coarse versioning, as it's so useful for on a Windows server with VSS. An in-filesystem snapshot faclility would be really, really nice for this sort of thing, and one that didn't require loopback mounts (instead providing virtual directory access or the like) would be truly fantastic for backups.

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VSS = Visual SourceSafe?

Posted May 13, 2010 11:44 UTC (Thu) by tialaramex (subscriber, #21167) [Link]

If that's the correct expansion, just say no. It should be a give away when you find you need "coarse versioning" for your version control system that what you have is a liability. Rather than thrash around trying to find ways to keep VSS sort-of working it should be a priority to migrate away from it.

This isn't some partisan thing, I don't care if you migrate to git or Perforce or even Team Foundation Server. But get off Visual SourceSafe. Once you're safely running a real version control system you'll find that your headache goes away without any need for "coarse versioning" using snapshots.

VSS = Volume Shadow copy Service (Yes, I know)

Posted May 13, 2010 13:27 UTC (Thu) by ringerc (subscriber, #3071) [Link]

Argh! That acronym collision drives me nuts.

Here, VSS = "Volume Shadow copy Service". Yes, Microsoft uses the acronym "VSS" for Volume Shadow Copy Service despite having an existing claim on that TLA via Visual Source Safe ie VSS.

You'd think they'd refer to it as VSCS, but no....

What I'm talking about is a facility in Microsoft servers (and client operating systems, but it's less important there) that's based on the Volume Shadow Copy Service where they can make automatic snapshots of their file systems on a schedule, and retain them until the total size of all snapshots reaches an admin-configured limit, at which point the oldest snapshot is dropped to make room.

The same underlying snapshot service is used to provide efficient image-based backup. In fact, on Win2k8 you can have the server maintain a bootable backup disk image of its self on a raw disk - I use an iSCSI volume on my Linux backup server. The server uses the volume shadow copy service to only update dirty parts of the image at each backup run. It's nice to have for a Windows-based server OS where unlike Linux/BSD you can't just rsync the whole file system contents to another box and expect to be able to boot it.

(For what it's worth, I use svn heavily, though am drifting git-wards now that I've started actually using it and discovered how seriously nice it is these days. You won't catch me near Visual Source Safe unless it's with an axe. In an amusing confluence of these two topics, I now maintain all my servers /etc in git and git-push them to the backup server every night, 'cos it's more convenient than Bacula when reverting changes).

VSS = Volume Shadow copy Service (Yes, I know)

Posted May 13, 2010 13:48 UTC (Thu) by nye (guest, #51576) [Link]

>Here, VSS = "Volume Shadow copy Service". Yes, Microsoft uses the acronym "VSS" for Volume Shadow Copy Service despite having an existing claim on that TLA via Visual Source Safe ie VSS.

>You'd think they'd refer to it as VSCS, but no....

That would be 'Volume Snapshot Service', supposedly. The acronym collision probably never occurred to anyone at Microsoft since (it is widely held, at least) nobody at Microsoft actually uses Visual Source Safe.

It's one of those things that was bought, mangled, and re-released to fill a gap in their product line, targetted at those people who must use all-Microsoft, all-the-time even if MS themselves think the tool is worthless.

The Next3 filesystem

Posted May 14, 2010 15:36 UTC (Fri) by mebrown (subscriber, #7960) [Link]

BTRFS has exactly what you describe (VSS) at the filesystem level, and is widely held to be the heir-apparent of the Linux Filesystem of the Future(TM) crown.

In fact, in Fedora 13, there is a yum plugin that will snapshot the system before every yum transaction, meaning you can rollback to any previous system state if an upgrade goes awry.

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