On 09/04/18 22:15, Vincent Royer wrote:
Thanks,

The 3 servers are new Lenovo units with redundant PS backed by two huge UPS units (on for each bank of power supplies).  I think the chances of losing two nodes is incredibly slim, and in that case a Disaster Recovery from offsite backups would be reasonable.

My requirements are about 2TB, highly available (so that I can reboot one of the 3 servers without taking down services).

Beyond that my focus is high performance for small I/O.
This can be a difficult case for GlusterFS, if you mean "small files", as the metadata lookups are relatively costly (no separate MDS with in-memory or memory cached database). It's ideally placed for large files, and small I/O within those files should be OK. just speaking from experience - should be fine for VMs with such loads, especially if you shard.

So I could do a single 2TB SSD per server, or two, or many more if that is "what is required".  But I don't want to waste money...

Resilience is never a waste. Skimping may well prove to be a waste of *your time* when you get woken up at 3am and have to fix a downed system. Your call entirely. I'm too old for that kind of thing, so I tend to push for both per-server and per-cluster redundancy. It usually gets approved after something "unexpected" happens the first time.

Gluster and ZFS will be fine with onboard controllers. If you have enough ports you'll be just fine. If you need more buy HBA's to stick in your PCIe slots, M1015s and M1115s on ebay perform very well and are still dirt cheap.

So are you using ZFS to get compression and checksumming down to the disk platter level? ZFS will give some gains in performance with compressible data and corruption protection, but, don't bother with dedup, I've tried it on 3 distributed filesystems and it bought less than 3% capacity and slammed performance. If you don't need either feature just stick with XFS for single-disk or software-RAIDed mirrors per brick. My personal opinion would be do a ZFS mirror of two SSDs per server, per brick, ie in your initial case, 2x2TB SSD per box in ZFS mirror. You can add more mirror sets later to add additional bricks.


I like the idea of forgoing the RAID cards as they are quite expensive, especially the capacitor backed ones.  The onboard controller can handle JBOD just fine, if Gluster is OK with it!

As I also said, if said expensive card dies, and you don't have another one in stock, you will effectively have lost everything on that server until you can source a new one (or even /if/ you can).

Use the power of the software to get where you need to be, the tools are there...

Alex

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