UFS2 snapshots on large filesystems

Xin LI delphij at gmail.com
Sun Nov 13 10:04:38 PST 2005

On 11/5/05, Scott Long <scottl at samsco.org> wrote:
> The UFS snapshot code was written at a time when disks were typically
> around 4-9GB in size, not 400GB in size =-)  Unfortunately, the amount

s/size/cylinder groups/g :-)

> of time it takes to do the initial snapshot bookkeeping scales linearly
> with the size of the drive, and many people have reported that it takes
> considerable amount of time (anywhere from several minutes to several
> dozen minutes) on large drives/arrays like you describe.  So, you should
> test and plan accordingly if you are interested in using them.

I have some ideas about lazy snapshotting.  But unfortunately I don't
have much time to implement a prototype ATM, and I think we really
need a file system that is capable for:
 - Handling large number of files in one directory (say, some sort of
indexing mechanism, etc.  And yes, I know that this is somewhat
insane, but the [ab]use is present in many large e-mail systems that
uses mailbox)
 - Effective recovery.  Personally I do not buy journalling much, and
I think the problem could be resolved by something like WAFL did.

I think that JUFS would provide some help for (2), do you have some
plan about (1)?

Xin LI <delphij at delphij.net> http://www.delphij.net

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