running mksnap_ffs

[Scott Oertel]

Kris Kennaway wrote:
> On Tue, Jan 02, 2007 at 09:06:24PM +0100, Willem Jan Withagen wrote:
>   
>> Hi,
>>
>> I got the following Filesystem:
>> Filesystem    Size    Used   Avail Capacity iused     ifree %iused 
>> /dev/da0a     1.3T    422G    823G    34%  565952 182833470    0%
>>
>> Running of a 3ware 9550, on a dual core Opteron 242 with 1Gb.
>> The system is used as SMB/NFS server for my other systems here.
>>
>> I would like to make weekly snapshots, but manually running mksnap_ffs 
>> freezes access to the disk (I sort of expected that) but the process 
>> never terminates. So I let is sit overnight, but looking a gstat did not 
>> reveil any activity what so ever...
>> The disk was not released, mksnap_ffs could not be terminated.
>> And things resulted in me rebooting the system.
>>
>> So:
>>  - How long should I expect making a snapshot to take:
>> 	5, 15, 30min, 1, 2 hour or even more???
>>     
>
> Yes :) Snapshots were not designed for use in this way (they were
> designed to support background fsck and allow faster system recovery
> after power failure), so they don't scale as well as you might like on
> large filesystems.
>
> Kris
>   


If snapshots were designed to support background fsck, then why did they 
not make it more scalable? If you can't create a snapshot without the 
system locking up, that means fsck won't be able to either, making 
background fsck worthless for systems with large storage.