[Need advice] Best Filesystem-Layout

[MaxR]

Im planning to run Proxmox on a rented Server with three SATA-SSDs ( Micron 1100s to be precise)
The question is what amkes more sense: two pools with one vdev each ( 1x single disk, 1x mirror=
or one pool with one vdev in RAIDz1.

Ive only ran ZFS on HDDs so far where my choice would be the mirror because of the iops-gain over RAIDZ1 but im not familiar if the same rule of thumb also applies to SSD-only deployments.

THanks for your help in advance.

 

[alexskysilk]

Ideally you'd want 4 drives to have a proper 2vdev striped mirror. with 3 drives your options are more limited.

I was thinking about this and I have a stupid idea for you. I dont know if I would go to production with such an config, but in theory it should work.

1. partition your drives to two equal size partitions, yielding 6 partitions.
2. create a mirror with the following vdevs:

tank
mirror-0
/dev/sda0
/dev/sdb0
mirror-1
/dev/sdc0
/dev/sda1
mirror-2
/dev/sdb1
/dev/sdc1

you'll have the performance of a striped mirror with 50% of your total usable capacity.

 

[guletz]

ank
mirror-0
/dev/sda0
/dev/sdb0
mirror-1
/dev/sdc0
/dev/sda1
mirror-2
/dev/sdb1
/dev/sdc1

you'll have the performance of a striped mirror with 50% of your total usable capacity.

But it will be a big problem with with any VM!!!! Think that for example you will use a 4 k vblock size, that will be split on 3 mirror, like: 4k/3. Then you will have for any write op a rwm for each block on SSD.

 

[LnxBil]

Ive only ran ZFS on HDDs so far where my choice would be the mirror because of the iops-gain over RAIDZ1 but im not familiar if the same rule of thumb also applies to SSD-only deployments.

If you want redundancy (yes, you want!) and you have only these three SSDs and cannot change anything, just go with a RAIDz1 and it'll work just fine.

 

[alexskysilk]

But it will be a big problem with with any VM!!!! Think that for example you will use a 4 k vblock size, that will be split on 3 mirror, like: 4k/3. Then you will have for any write op a rwm for each block on SSD.

Thats not how that works. Each block is written to one vdev at a time, which is why performance is so superior on a zfs mirror then a parity set. The downsize is that vdevs can fill up at unequal rates despite zfs doing its best to keep them balanced leading to inconsistent performance, but this is typical of all zfs multi vdev sets as they get full.

 

[MaxR]

Ideally you'd want 4 drives to have a proper 2vdev striped mirror. with 3 drives your options are more limited.

...

Thanks, I guess i might give this a try, although it goes against the rule of thumb not use use partitions whenever possible.