Disks with different sizes and controllers

G

Graaf_van_Vlaanderen

I'm currently converting my old PC to a file server.
The PC has four hard drives:

1. SATA 80GB: already installed FreeBSD with ZFS on this drive.
2. SATA 250GB
3. SATA 500GB
4. PATA 160GB: connected on the Asus motherboard (P5KR) through a JMicron controller.

Questions:

1. Considering the different sized disks, what would be the best "mirror" layout.
I was thinking of mirroring the second disk with half of the third one, and the other half of the third one with the fourth one.
2. Is this ZFS mirroring going to work fine with the fourth drive?
 
You really shouldn't mix disk types (IDE/SATA) within the same vdev (mirror, in your case). The speed of the vdev will be limited to that of the slowest device in the vdev. IOW, your SATA disk will be "limited" to IDE speeds, as you cannot write anything to the faster disk(s) until the slower disk is finished.

You'd probably be better off using the 160 GB disk as a bulk storage or backups disk, and not use it as part of any mirror vdev.

Then create a GPT partition on the 250 GB disk. And 2 GPT partitions on the 500 GB disk (each 250 GB in size; make sure the size of the first partition matches that of the 250 GB disk). And create a ZFS mirror vdev with the first partitions on each disk.

Then, if you want, you can use the "extra" 250 GB as scratch space.

Or, if performance really doesn't matter, you can (be sure to label the partitions):
  • create GPT partition on the 160 GB disk
  • create GPT partition on the 250 GB disk
  • create 250 GB partition and 160 GB partition on 500 GB disk/list]
    Then:
    1. # zpool create mypoolname mirror gpt/160-disk gpt/160-partition
    2. # zpool add mypoolname mirror gpt/250-disk gpt/250-partition
That way, you have two mirror vdevs, one 160 GB in size, one 250 GB in size, striped together into one pool.

The downsides are that performance won't be that great due to head-thrashing and disk contention on the 500 GB disk, and if you lose the 500 GB disk, both mirror vdevs are then degraded.
 
Thanks for the feedback. I've already created two separated mirror pools.

The performance won't be really affected since it's for a home file server and I'm only writing at one mirror at the same time.

Yesterday I copied all my Images over the network and achieved speeds up to 100MB/s!
Average speeds were way over 40MB/s.

As soon as the hard disk prices are down again, I'm planning to add some bigger equal sized drives.
 
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