Optimized Disks

[kspare]

Just some sunday thinking from some reading i've been doing.

I've currently got my freenas box setup with the following:
24 2tb WD Black Drives
12 Mirrored Vdevs
1 Intel 400gb 750 PCI SSD for SLOG
another for L2Arc
64GB Ram
Dual 10gb Nic
Running iscsi.

we're hitting 35% on our l2 hits and 85 on arc hits.

I thought about trying two options:

Change to 2 12 drive stripes mirrors (aka 0+1)
Or try 3 Raidz's with a 3 way mirror.

Has anyone played with this?

The primary purpose for this machine is VM's and particularly file servers.

My thought about the raidz was that I would gain more storage and help keep fragmentation down. but that all depends on the performance hit of course.

My other thought has to do with the performance of the Arc and l2arc.

Would NFS not performance better being that it would be at file lever vs iscsi at the block level? Would this not be an advantage of NFS?

Also when thinking about fragmentation being that nfs is file level when removing snapshots etc and shinking the space you use wouldn't think help with fragmentation issues as well?

 

[tvsjr]

Striped mirrors, as you appear to be currently configured, will provide the best performance. If this box is heavily used for VMs, then IOPS are king... you get a sum of the IOPS of the slowest device in each vdev. You've got 12 vdevs right now... around 1200 IOPS. Any other configuration will mean less vdevs, and less iops.

You also appear to be lacking in the RAM department... since you're running an E5, I assume you've got substantial room for growth, unless you have some SFF motherboard. RAM is cheap - max it out.

When trying to address performance issues, it's very important that you understand a. what the issue is, b. what you intend to try, and c. how you believe that attempt will solve the issue. Unless you have committed a horrible design sin, making wholesale changes to your design without first understanding the problem is roughly equivalent to shooting in the dark.

 

[Robert Trevellyan]

Change to 2 12 drive stripes mirrors (aka 0+1)
Or try 3 Raidz's with a 3 way mirror.

I'm confused about the alternatives layouts you're proposing. Just to recap the basics, a mirror is a type of vdev. You can stripe vdevs, i.e. make a pool from multiple vdevs, but you can't mirror vdevs.