UFS2 snapshots on large filesystems
scottl at samsco.org
Fri Nov 4 14:07:27 PST 2005
> Considering a PC server running FreeBSD with 4 400 GB hard drives attached
> to a hardware raid controller doing raid-5.
> So this will present itself to the OS as a 1.2TB filesystem.
> Any comments on taking one or multiple snapshots of a filesystem of this
> size ?
> Given current disk capacities, I would not exactly consider this 1.2TB
> filesystem a "large" one ... any comments on say ... a 6-8 TB filesystem
> and making one or more snapshots of it ?
> Assume they are marginally busy - perhaps a 5-10% data turnover per day...
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
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.
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