16x 3TB backup server - RAID-Z2?

[leonroy]

Wondering if RAID-Z2 would be doable for a 16 x 3TB server hosting backups?

It'll be holding a combination of backups from our primary FreeNAS box (which is RAID-10) as well as Veeam backups from vSphere.

Box has 32GB RAM and a reasonable SSD SLOG device.

Hard drives are mixed brand 3TB SATA disks. WD Reds, Toshibas and some Seagate Barracudas.

 

[Bidule0hm]

It's not recommended to go over 11-12 drivers per vdev.

I recommend 2x RAID-Z2 vdevs of 8 drives each ;)

 

[Robert Trevellyan]

I recommend 2x RAID-Z2 vdevs of 8 drives each

+1

Box has 32GB RAM and a reasonable SSD SLOG device.

Not clear to me why you would need a dedicated SLOG device on a backups server.

 

[leonroy]

Thanks guys, will proceed with that layout then.

Not clear to me why you would need a dedicated SLOG device on a backups server.

Two reasons really:

1. It only adds 10% to the cost of the box and future proofs the server in case needs change.
2. We host our VMware Backup Appliance on a NFS share on the backup server. VMware's NFS writes are sync only hence why we need it.

 

[Robert Trevellyan]

We host our VMware Backup Appliance on a NFS share on the backup server. VMware's NFS writes are sync only hence why we need it.

Thanks for clarifying.

1. OK.
2. The way I understand it, a dedicated SLOG is indicated when sync writes are used and performance isn't good enough without it, i.e. when sync writes go directly to the pool. Is that your situation?

Not a gotcha, I'm trying to learn.

 

[leonroy]

The way I understand it, a dedicated SLOG is indicated when sync writes are used and performance isn't good enough without it, i.e. when sync writes go directly to the pool. Is that your situation?

Sync writes indeed hit the SLOG. In our usage (Windows (SMB), Macs (AFP) and VMware ESXi Hosts (NFS) only VMware uses sync writes.

Here's a very good article on the subject.

 

[Robert Trevellyan]

Sync writes indeed hit the SLOG.

I understand that. The reason for my question is that you don't have to have a dedicated SLOG to have sync writes, it's just that without one they go directly to the pool. The purpose of the SLOG is to improve IOPS for sync writes. In the article, which I have read before but not studied for this particular issue, Aaron says, "you will see improved disk latencies, disk utilization and system load. What you won't see is improved throughput. Remember that the SLOG device is still flushing data to platter every 5 seconds." So I'm curious about whether a backups workload really benefits from a dedicated SLOG. VM hosting, for sure, but backups?

 

[leonroy]

VM hosting, for sure, but backups?

We run a VMware backup appliance which is essentially a virtual machine. It resides on our backup appliance and stores it's virtual disk on there. Hence why we need a SLOG. Besides Intel SSDs are cheap enough that we stick one in every file server we build to act as SLOG.

 

[Robert Trevellyan]

Got it, thanks!