Starwind HA, combine SSD and SAS storage

lohelle · Sun Aug 28, 2011 2:15 pm

I have a design question. I do not know if my thinking is correct, so please comment.

I'm thinking of trying something like this if this works the way I hope it will:

Server 1 (primary) with 16x 256GB SSD (MLC), utilizing maybe 200GB of each. No RAID, just single drives as LUN's.

Server 2 (secondary) with (my existing) 16x 450GB 15k SAS-drives in RAID 10

If I design a HA solution with the SSD's as primary, can I use fixed paths in vSphere to get the awesome read IO of the SSD's ? Or will the SAS drives on HA-node 2 slow me down?
And for writing (the IO is primarily reading), will the write cache on HA-node 2 allow for short fast bursts to the VM's (where the SSD's will be able to cope, but the SAS-drives needs the help of the cache)

If this works as I hope, I can design a rather cheap solution with great performance.

lohelle · Mon Aug 29, 2011 8:57 pm

To be clear. I want to use Starwind HA to have a replica of my SSD datastores, but I do not want to use SSD's on the secondary HA node. Reads should primarily go from the SSD HA-node, so no RR load balancing (but failover to the other HA node if the primary goes down).

Tue Aug 30, 2011 2:30 pm

You can do in *theory* what you want. But you need to take care of a few things 1) you need to allocate HUGE amount of write-back cache at both nodes. To compensate fast write on SSD and slow write on HDD and 2) make sure your scenario is so-called "pulsating" one. In the other words - writes are followed by some inactivity time so system has time to flush cache to disk and finally 3) you have more reads then writes if 2) cannot be achieved. So for some scenarios say virtualized Exchange or Lotus Notes you may have everything working fine but for some cases like heavy load SQL Server you may have slowest spindle based node as a break of your whole cluster.

lohelle · Tue Aug 30, 2011 2:52 pm

Thank you for the reply.
The load is actually not going to be very high, but I want high performance for the terminal services VM's. I think average load will be very low, with short bursts only.

I have 2 SSD datastores now with a single SW host, and the performance of the few VM's hosted on these SANs are A LOT better than the SAS-hosted VM's. And the SAS-drives are 16-disk RAID10 (vs single drive SSD)

Tue Aug 30, 2011 10:05 pm

If load is going to appear / disappear in bursts only then you should be fine with fixed path config.

However upcoming versions of StarWind will have automatic data tiering so hybrid SSD / spindle nodes should shine.

lohelle wrote:Thank you for the reply.
The load is actually not going to be very high, but I want high performance for the terminal services VM's. I think average load will be very low, with short bursts only.

I have 2 SSD datastores now with a single SW host, and the performance of the few VM's hosted on these SANs are A LOT better than the SAS-hosted VM's. And the SAS-drives are 16-disk RAID10 (vs single drive SSD)

lohelle · Fri Sep 02, 2011 5:45 pm

I did a quick test, and this works just as I hoped.

When I use fixed path to the SSD HA-node I get very nice IO ( >= 4000 read AND random IOs). When using the SATA -path I get <=500 IO's).
Write speed is now limited by my 1Gbit sync channel. Is it possible to use more than one nic for sync?

I might consider a 10Gbit NIC, but i might just team some nics..

This setup lets me use fast "unreliable" desktop SSD's as primary target, and if one failes the VM's will continue to run on the second node..

Sat Sep 03, 2011 10:52 am

To use more then 1 NIc for sync in current release you need to make your NICs teamed

lohelle · Wed Sep 21, 2011 5:06 pm

I will just update this after some days of usage.

This solution works GREAT! Database performance is MANY TIMES better than before for some workloads because of the SSD drives.
I present single SSD's (image file) as single LUN's, with the SAS server as secondary.

The only catch in this design is that I can only use a single IO path in Vsphere. It I change to RR LB it will also use the "slow" paths. It would be great to be able to choose 2 out of 4 paths in Vsphere.

Thu Sep 22, 2011 8:56 am

Thank you very much for keeping us updated! Nice to hear you're doing great

Do you need any kind of assistance from StarWind side to make listed scenario (2 from 4 paths) work?

lohelle wrote:I will just update this after some days of usage.

This solution works GREAT! Database performance is MANY TIMES better than before for some workloads because of the SSD drives.
I present single SSD's (image file) as single LUN's, with the SAS server as secondary.

The only catch in this design is that I can only use a single IO path in Vsphere. It I change to RR LB it will also use the "slow" paths. It would be great to be able to choose 2 out of 4 paths in Vsphere.

lohelle · Thu Sep 22, 2011 8:27 pm

Is it possible from Vsphere to use more than 1 fixed path? I thought i could only choose RR (all paths) or fixed (one path). MRU is also just one path I think.

I have 4 paths to the fast SSD storage and two to the "slow" SAS storage. Is it possible to use the 4 paths (RR) to the SSD storage and only use the SAS-paths as failover?

Thu Sep 22, 2011 8:34 pm

Can you use NIC teaming to solve this task? So one virtual adapter would aggregate both physical paths you'd like to use?