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Network RAID 5 storage utilisation - SAN/IQ 9.5

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TheVillag3Idi0t
Occasional Visitor

Network RAID 5 storage utilisation - SAN/IQ 9.5

Hi folks,

 

Wondering if anyone can answer this definitively, or at least point me in the right direction...

 

I am interested in creating volumes based on Network RAID 5, particularly for file shares in order to save a bit of space rather than using Network RAID 10, but when i create the volume (thin provisioned) and check the "Volume Use" area of the cluster, it initially reports a saving of exactly twice that of the size of the volume, implying that it would consume the same capacity as if i configured it with Network RAID 10.

 

Just trying to work out how much space i will have available in the cluster once i have configured all of my volumes, but having a hard time reconciling the utilisation of the NR 5 volumes...

 

Is this normal behaviour? Are there no storage savings to be gained utilising Network RAID 5?

8 REPLIES
JohnMurrayUK
Advisor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

Yes, that is to be expected.  The CMC used to report the provisioned space nicely to make this clear but now it just states the reported size and consumed space.  

 

Due to the odd way SANiQ implments these Raid levels, NRaid5 and NRaid6 require snapshots to deliver the expected space saving.  If you have an NRaid5 volume with no snapshots, its space profile is the same as NRaid10.

 

NRaid5 is really a thin provisoned NRaid10 volume with a snapshot.  Behind the scenes (AFAIK), snapshots are taken which are written using actual NRaid5 and hence some parity.  Don't forget that when a snapshot is created the original volume reports (or at least used to report) the actual snapshot provisioned space and that the original volume all of sudden only had a few MB of space provisioned.  i.e. the action of taking a snapshot means the real data is moved into the snapshot and re-striped as NRaid5 (you can see the restriping process in the GUI), leaving only the new writes occuring as NRaid10.

 

I struggle with this myself as the HP Storage Sizing Tool still lists the capacity the traditional way, i.e. for a 10TB NRaid5 volume, you would need 15TB of usable disk space, which is just not quite the case if you have a lot of writes.

 

Anyway HTH

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TheVillag3Idi0t
Occasional Visitor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

Hi John, thank you for taking the time to respond to my question, greatly appreciated. I think that in the past, snapshots were required for space savings with NR5 volumes, but since version 9 i dont believe this is the case anymore.

 

From this link, http://bizsupport1.austin.hp.com/bc/docs/support/SupportManual/c01886197/c01886197.pdf, it states that version 9.0 includes "Network RAID 5 and 6 enhancements - no longer requires snapshots"...

 

Interestingly enough, i created a 1.3TB NR5 (thin) volume and wrote just over 900GB of data into it, it is reporting that the consumed space is 1.2TB, which seams to be more inline with the utilisation i was expecting...

 

I'm really just trying to work out how much capacity i'm going to have left over (if any!) once i provision all of my volumes, but the way it reports cluster utilisation is making the task difficult...

Bart_Heungens
Honored Contributor
Solution

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

Hi,

 

The amount U can use (or loose) depends on the amount on nodes in your cluster... For RAID 5 the minimum nodes is 3 (obvious for RAID 5), the maximum is 5 nodes... So when U select Network RAID 5 there will be 4 data blocks and a parity block on the 5th node... So U will loose 20% of total capacity...

 

 

Kr,

Bart

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Dan Nichols
Advisor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

I think that the version 9 notes should say "no longer exposes NR5 snapshots in the GUI". I believe that the snapshots are still taken behind the scene just not visbile in the GUI as support were have issues with customers disabling/altering snapshot schedules in v8.5.
TheVillag3Idi0t
Occasional Visitor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

Thanks to all for your responses. If there are indeed snapshots still being taken in the background, i will have to read some more documentation to get my head around what is going on behind the scenes.

 

We currently have a four node cluster, and each N-RAID5 volume seems to be taking approximately 1.3x the configured size, which makes sense.

 

Thanks again for the help.






JohnMurrayUK
Advisor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

The snapshots occur in the background every 10GB or 10% of change AFAIK.  You can see the restriping happen if you dump a file on a volume.

I'm not a fan of this hidden aspect, but it prevents people from removing the last snapshot and hence reverting the volume to Network Raid 10.

I'd rather see it more transparently, and ideally with configurable parameters to perhaps postpone restriping to quiet periods or at least deprioritise them further depending on need.

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M_C
Occasional Advisor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

 

Are you sure it still uses background snapshots. The release notes specifically say they have removed the need for snapshots.

 

I have done some testing and I do lose about 25% is write performance as soon as I enable this (1GB write) which indicates it is not writing normally then committing the snapshots.

 

I would log a ticket with HP but I know what they will say - "No snapshots" but it will just be a first line guy reading the notes as I have.

 

 

Bart_Heungens
Honored Contributor

Re: Network RAID 5 storage utilisation - SAN/IQ 9.5

From what I understood (but I am not the developer), there are indeed no snapshots anymore in the background...

 

Kr,

Bart

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