Cobbling together various SSD disks

All your general support questions for OpenZFS on OS X.

Cobbling together various SSD disks

Postby Sharko » Sun Sep 20, 2020 12:36 pm

Hi, I've been using a single 2TB SSD for my main zfs pool. It's not ideal, since there is no redundancy, and if the SSD fails I'll have to fall back to a backup. I do have a robust, multi-level backup strategy, which is how I've justified the risk (which is probably relatively low anyway). However, it has occurred to me that I could juggle some other SSDs around, and combine them all into a mirror pool to get redundancy. What I've got, in addition to the 2TB pool, is a pair of Micron 960GB SSDs.

Suppose I were to split the 2TB SSD into two partitions. Let's suppose that this results in the two partitions being called disk1s1 and disk1s2. We also have the two 960GB SSD devices in the SATA bays, and these are assigned disk2 and disk3. Would it be possible / advisable to form a zpool that pairs one partition with one of each of the smaller disks, like so (skipping the finer details of normalization, case-sensitivity, ashift, etc):

Code: Select all
 % zpool create TANK mirror disk1s1 disk2 mirror disk1s2 disk3

So, this would pair up a partition of the 2TB SSD with one 960GB (resulting in a 960GB mirror VDEV), and a second partition of the 2TB SSD with the other 960GB SSD. If one of the 960GB SSDs fails, there is redundant data in the corresponding 2TB partition, and if the 2TB SSD fails it takes out both partitions but the two 960GB SSDs still have redundant data to carry the load. Does anyone see a problem with this scheme? Obviously it uses up 3 SATA bays, which is not ideal, but it seems like I would gain security. It all hinges on whether it is a good idea to pair up a partition with a disk; I've put zpools on partitions in the past on my laptop, but never used them in mirrors.

Thank you for your advice.
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Re: Cobbling together various SSD disks

Postby tangles » Mon Sep 21, 2020 12:36 am


You could do what you want I guess…

I certainly wouldn't do it…

Seeing though you appear to have a sound backup strategy in place already, I know what I'd be doing…

I'd stripe those two SSDs and watch your I/O fly! Then just use the old 2TB clunker for snapshots…


If you really want to use the 2BT as part of your main/primary pool, then I'd wait for OpenZFS 2.0 be released by the Linux guys, (RC1 came out a month ago, definitely happening this year) and then wait for Lundy to push the macOS changes into the tree.

OpenZFS 2.0 gives you more control over vdevs as to what they store (i.e. metadata v data blocks) and so you could get more storage and faster performance this way… (again no redundancy which I'm not overly comfy about still).
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