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ZFS ssd pool... any gotchas?

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farscapesg1

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With luck, I'll be picking up a couple more 240GB SSD drives to build a 4 disk RAIDZ pool to move my home VMs to. Any gotchas or worries to plan for? The main VMs running in my home lab are...
1. Untangle box
2. Windows 7 DVR (was SageTV, trying WMC... but they record to a iSCSI share on a spinning disk pool)
3. Torrent/Usnet box (downloads to shared storage on a spinning disk pool)
4. Server 2012 Essentials (backs currently go to storage on a DroboPro via iSCSI)
5. Plex server (pulling files from the shared storage pool)

I've got a couple other systems for ripping disks and running handbrake and plan on spinning more test systems up soon, but those are the "always on" ones. I think I have them pretty well configured to minimize any SSD usage on the new pool.

The storage server and ESXi server is on an APC 1400 UPS with sync writes disabled for the spinning disk pool. My plan is to enable sync writes for the SSD pool since the IOPS are a lot higher. I haven't decided if I can squeeze everything into 480GB and run as a stripped mirror, or just go for the extra space and do RAIDZ, but either way the performance should be better than my 6-disk stripped mirror of spinning disks.
 
You are running mostly OSes on the SSD pool, so you need IOPS more than sequential speed. I think mirroring is the way to go.

Anyway, you can test both. Just ZFS send the SSD pool contents to your spinning pool, rebuild the SSD pool in different configuration and ZFS send the OS drives back. In order to do this, I would not put anything in the root filesystem of the pool. Make a sub ZFS that you can move from pool to pool.
 
I'll try out the both configs.. but I'm thinking the IOPS on a single SSD is still so much higher than a 6-disk stripped mirror, even with sync writes enabled, that there won't be a comparison. Considering these drives are spec'd for 39k read IOPS and 83k write... while 7200 RPM hard drives provide about 100 IOPS, I doubt IOPS will be much of a concern.

I guess what I'm wondering is if there are any tweaks I need to make to the pool settings to cover TRIM and/or try to extend the life of the drives.
 
A RAIDZ/Z2 pool with SSDs should provide enough IOPS for multiple VMs unless you need obscene amount of IOPS. But depending on your zvol block size you could waste a lot of space with improper or to large disk counts.

Depending on the importance of the VM images I would buy SSDs with power loss protection even if you use an UPS. There is a reason why all enterprise SSDs have PLP even though actually it is the enterprise systems that commonly use UPS.
 
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