[gpfsug-discuss] Can't take snapshots while re-striping

[Luis Bolinches]

And use QoS 

Less aggressive during peak, more on valleys. If your workload allows it. 

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Luis Bolinches
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> On 18 Oct 2018, at 19.13, Alex Chekholko <alex at calicolabs.com> wrote:
> 
> The re-striping uses a lot of I/O, so if your goal is user-facing performance, the re-striping is definitely hurting in the short term and is of questionable value in the long term, depending on how much churn there is on your filesystem.
> 
> One way to split the difference would be to run your 'mmrestripe -b' midnight to 6am for many days; so it does not conflict with your snapshot.  Or whatever other time you have lower user load.
> 
>> On Thu, Oct 18, 2018 at 8:32 AM Peter Childs <p.childs at qmul.ac.uk> wrote:
>> We've just added 9 raid volumes to our main storage, (5 Raid6 arrays
>> for data and 4 Raid1 arrays for metadata)
>> 
>> We are now attempting to rebalance and our data around all the volumes.
>> 
>> We started with the meta-data doing a "mmrestripe -r" as we'd changed
>> the failure groups to on our meta-data disks and wanted to ensure we
>> had all our metadata on known good ssd. No issues, here we could take
>> snapshots and I even tested it. (New SSD on new failure group and move
>> all old SSD to the same failure group)
>> 
>> We're now doing a "mmrestripe -b" to rebalance the data accross all 21
>> Volumes however when we attempt to take a snapshot, as we do every
>> night at 11pm it fails with  
>> 
>> sudo /usr/lpp/mmfs/bin/mmcrsnapshot home test
>> Flushing dirty data for snapshot :test...
>> Quiescing all file system operations.
>> Unable to quiesce all nodes; some processes are busy or holding
>> required resources.
>> mmcrsnapshot: Command failed. Examine previous error messages to
>> determine cause.
>> 
>> Are you meant to be able to take snapshots while re-striping or not? 
>> 
>> I know a rebalance of the data is probably unnecessary, but we'd like
>> to get the best possible speed out of the system, and we also kind of
>> like balance.
>> 
>> Thanks
>> 
>> 
>> -- 
>> Peter Childs
>> ITS Research Storage
>> Queen Mary, University of London
>> 
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