[Linux-cluster] GFS Tunables

[Gordan Bobic]

Steffen Plotner wrote:

>> Kevin Anderson wrote:
>>> On Thu, 2008-10-16 at 21:29 +0100, Gordan Bobic wrote:
>>>> Brandon Young wrote:
>>>>
>>>>> As for LVM snapshotting ... I am under the impression that those 
>>>>> features are unavailable in GFS (and are slated for GFS2? 
>>  Which is 
>>>>> not "production ready", yet?)  It has certainly occured 
>> to me to try 
>>>>> that feature, if only it were available.  Am I 
>> misinformed?  Perhaps 
>>>>> I need some more education on how exactly LVM mirroring will help 
>>>>> me.  I am
>>>>> *attempting* to approximate a traditional backup scheme, 
>> atleast on 
>>>>> this particular filesystem.  Am I correct in believing 
>> that I could 
>>>>> snapshot a volume (assuming the feature is available) and run a 
>>>>> traditional backup (using, say, rdiff-backup) in a 
>> shorter time than 
>>>>> I can now, where I'm running it straight off a live GFS volume?
>>>> You can use CLVM (Cluser aware LVM) and create GFS on top of that 
>>>> volume. You can them use CLVM to take a snapshot of the 
>> block device, 
>>>> mount it read-only with lock_nolock and back that up. That 
>> should go 
>>>> at non-clustered FS speeds.
>>>>
>>> We don't have support for cluster snapshots as of yet even 
>> though it 
>>> has been on the todo list for about 5 years now :(.
>> Joy... My mistake. Sorry I mentioned it.
>>
> 
> How about snapshotting at the backend storage device? We usually use
> linux as the backed, hand out storage via iscsi and snapshot at the
> backend - this eliminates the need for doing snaps at the GFS level - I
> agree that if there was snapshotting at the LVM/GFS level we could get a
> clean snapshot.... another problem..

The problem with that being that you have your storage system as a 
single point of failure which rather defeats the point of clustering.

Gordan