MSA 2050 SAN - One Pool or better Two?

[M_Kunert]

Hello MSA Experts,

for a long time, our company used MSA 2040 SAN Enclosures providing LUN disk to an FC-storage system. Now we use MSA 2050 SAN … with these Pool A/B config.

Our “Storage solution” is located on multiple FC-Hosts, all using multipath FC connections for balancing and redundancy. As an example, one FC-HOST can have up to 4 FC-connections the same FC-LUN-Disk.
Our software is creating a raid-0 or raid-10 over all these accessible FC-LUN-Disks.

In MSA 2040 we created 2 RAID-6 disks each 6 disks (12 disk enclosure).

Now in MSA 2050 SAN, we do the same, but each RAID-6 is in a different POOL A/B.

I read already the HPE MSA Gen5 virtual storage – Reference guide, but for such a “simple” configuration I need, it is not easy to decide what is the “Best” option to choose.

It looks like
Controller A is controlling Pool A and
Controller B is controlling Pool B.
… In case one controller failed the other takes “temporally” care of the other Pool …

I like more the config if booth controller take care all the time for ONE POOL …
The reference guide is calling it “One Pool, with 100% headroom” …

Does someone know of “advantage” or “disadvantage” between this config?

“Pool A on Controller A (with only one - Archive - LUN disk) and
Pool B on Controller B (with only one - Archive - LUN disk)”

or
“Only Pool A on Controller A/B (one Archive – Tier 2 – with 2 LUN disk)”

Do we have a different cache usage with 2 Pools?

For me, the 2nd (single Pool) looks more like my old “linear” storage.
Any comment is welcome.

Best Regards,
Mathias

[Josh94K]

hello @M_Kunert 
I hope you are doing well. 

We have a similar discussion going on in the following community forum, please check it out. 
https://community.hpe.com/t5/MSA-Storage/One-or-2-storage-pools/td-p/7006199

@M_Kunert  I hope this helps! Should you have any additional query please let me know
If you feel this was helpful, Please HIT that KUDOS!  thumb below!

Note: "While I am an HPE Employee, all of my comments (whether noted or not), are my own and are not any official representation of the company."

[M_Kunert]

Hello Josh94k,

Thank you for the answer.

But the post you gave me (https://community.hpe.com/t5/MSA-Storage/One-or-2-storage-pools/td-p/7006199) is not enough for my case scenario. 

I also found this post (https://community.hpe.com/t5/MSA-Storage/MSA-2050/td-p/7074674) and the last message from  SUBHAJIT KHANBARMAN_1 make me nervous :

\\Regarding volume availability on both controllers, that's not possible. At a time volume will be owning by one controller only. In case of owning controller failure other controller will take over. \\

I need all-time availability of my 2 FC-LUN's on all controllers.

But if I put them into POOL A and B it sounds like I can access my LUN  2 (pool B) over controller A - only if controller B failed ...

I test this at the moment:

My (actually single) FC-Host has 2 FC-Ports and the 2nd FC-Port is only to controller A of the 2050 SAN enclosure connected - nothing on controller B - But I see and can access my LUN 1 (Pool A) and my LUN 2 (Pool B). 

So what is now correct?

I "only" need always 3.000 Mbit/s out of one enclosure - even if one controller failed, a rebuild was started or any other single failure was/is happend.

-> If I connect controller A and B will something block my access over controller A to Pool B (LUN 2)? -> in a 2 pool config.

Thank you for the support!

Best Regards,

Mathias 

[ArunKKR]

Hi Mathias,

The Pool A volumes will managed by controller A and Pool B volumes will be managed by controller B. 
The preferred path for Pool A volume data traffic is controller A host ports A1 A2 A3 A4. 
Similarly, the preferred path for Pool B volume data traffic is controller B host ports B1 B2 B3 B4.

If controller A fails/shut down/restarted , controller B will take ownership and data traffic for volumes in both Pools will flow through controller B host ports.

Pool A volumes will be sending traffic through controller B host ports which creates a small latency. 

When you have 2 Pools there will be controller level load balancing.

Each controller has its own cache.

The advantage of single Pool with 2 disk groups is that the load will be shared across all the disks. 

There is no single answer to the question which is best as you need to test each configuration in your environment and decide which gives optimal performance.

The maximum number of disks that you could have in a RAID 6 disk group as per power of 2 recommendation is 10.
This would give optimal sequential write performance.

Try to avoid software RAID at operating system level as it could create issues with volume repair at OS level, if a disk group fails.

If software RAID at operating system level is mandatory for your applications , I would suggest to use single Pool with multiple volumes under it.

Please refer pages 18/19 of MSA best practices guide:

https://psnow.ext.hpe.com/doc/a00015961enw?jumpid=in_lit-psnow-red

[ArunKKR]

Hi,

Please let us know whether the information shared helped.

[Josh94K]

Hello ! @M_Kunert 
Good day, 
just checking in to see if you have any further questions on MSA pool configuration. 
If Yes, please let us know, else you may mark this forum post as solved   

@M_Kunert  I hope this helps! 
If you feel this was helpful, Please HIT that KUDOS!  thumb below!

[JonPaul]

Hi Mathias,

In your setup you are using Software RAID (host RAID 0 or RAID 1) on top of hardware RAID (MSA Storage) this is great for availability when using RAID 1 software RAID.  In your 2040 setup when using 2 different Linear Storage Disk Groups (DG) you would have redundancy across 2 different RAID sets.  If you want to continue that then you want to use 2 Pools as with Virtual Storage (MSA 2050) your volume data will be spread across all DG in a pool and if you lose a DG then you likely lose data from every volume on the Pool. Eg your Software RAID would lose data from both sides of the mirror.  For your RAID 0 software RAID, a single Pool would probably be best.  You could see some performance benefit from using a volume from both Pools in RAID 0 but you would not see redundancy improvement, in fact you do the opposite of now being dependent on BOTH pools, every DG in the system.
The big benefit of using a single Pool is that you lower overhead, combine all spindles to get maximum performance from the backend disks and have consistent performance in a failover/controller down situation.  The controller cache benefits of using 2 Pools are quickly exhausted as each controller only has 4GB of cache.  If you have a lot of disks (multiple enclosures) or are using lots of SSDs then the performance of using both controllers(2 Pools) may be beneficial but at the expense of a controller down situation providing less performance to all volumes.