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Snapshot performance comparison EMC Celerra vs NetApp FAS

Posted on 2010-09-16
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I am comparing NetApp and EMC solutions for a VMware solution. The VMs will be on NFS. I know that EMC and NetApp use different methods of snapshots. Correct me if I am wrong on this, with EMC when a snap is made, all old data that is modified is written to hidden snap volume and the new data is written to the original location. With NetApp a pointer is put in the original data and the new data is written elsewhere. So with EMC there is a read operation and 2 writes, and with NetApp there are 2 writes although one of them will be small.

However though when it comes to reading that data, doesn't this mean that NetApp will have to make 2 read IOs to access the data, one for the pointer and one for the actual data? EMC will only have one read since the new data already replaced the old data. Does this sound correct?

Also from what my understanding is, with an NFS share EMC and NetApp will have roughly the same size usage by snaps?

Any real word experience with any type of performance impact having snaps of a file share running on an hourly basis for 2 days time would have with either system?

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Question by:ryan80
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by:paulsolov
ID: 33698650
I don't believe that Netapp has a penalty since the snapshot data is stored in the same volume (since only keeps pointers).  The snapshots for Netapp only take up room when there is a deletion of original data, there is no penalty for new data.    EMC and Netapp snapshtos work differently, from what I have been able to find and I may be in incorrect but Celerra is still copy on write which means that any changes are being written to a snapshot location.

On the Netapp CIFS shares I normally perform a snapshot every 1-2 hours with no percievable performance issues at all (setup for 36 hourly, 7 daily, and 4 weekly snapschedule).  Users can restore items on their own and see "previous versions" when right clicking on a file.  With deduplication the storage is smaller in size then the NTFS share that it originated from and snapshot usage is very limited in size even when dozens of snapshots are availalbe (up to 255)



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by:ryan80
ID: 33703125
I would think though that there would be an IO hit on reading current data since for every read that has to take place of data that has been snapped, it will have to make 1 IO to read the pointer (not a large amount of data, but still an IO) and then read the current data from the other location.

From what I see EMC will not have the read performance hit, but will have a bigger performance hit when taking the snap. It will have to read the data being changed, write the old data to the snapshot hidden location, and then write the new data. Now I don't know much but this sounds like it could take some time depending on the amount of changed data.
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paulsolov earned 500 total points
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On the Netapp it's still at the same location just that new data is also in the same volume as well.  In your environment (I have configured much larger environments) I have not see any performance issues.  If you are going to have SQL databases with high I/O on the VMs it is better to have them outside of the NFS volume by either using MS iSCSI, NPIV directly to LUN, or RDM.  Otherwise you should be ok.
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by:ryan80
ID: 33703296
No I am not concerned about the impact in my environment at all, just more curious about the differences between the two vendor types of snapshots.
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