zfs special device on boot ssds

[ray.]

Hi,

I am planing an proxmox backup server installation, with two 240GB ssds with zfs raid1/mirror and four 8TB hdds with zfs raidz1.
And since 240GB are way too much for the os, there should be enough space left over that can be used as special device for the hdd-pool.
Can i just add an zvol to the ssd-pool and use it as special device for the hdd-pool, or are there better solutions?

 

[guletz]

Can i just add an zvol to the ssd-pool and use it as special device for the hdd-pool, or are there better solutions?

Yes you can, .... but Do Not Do It ! In such a case this zvol will be part of your pool. If this zvol will be broken .... then your pool will say to you "Good by, your data is gone ..." . The second reson is performance(OS + zvol will not perform as you want), and your SSD life expectation will be less ....

Good luck / Bafta !

 

[ray.]

Yes you can, .... but Do Not Do It ! In such a case this zvol will be part of your pool. If this zvol will be broken .... then your pool will say to you "Good by, your data is gone ..." . The second reson is performance(OS + zvol will not perform as you want), and your SSD life expectation will be less ....

Good luck / Bafta !

Ok, redundancy should not be a problem since the ssd-pool the zvol is part of already is mirrored.
And since these are server grade ssd (samsung sm883), life expectation should not be a problem, too.
Is there a better way? Can something like this be achieved by using a single zpool with all 6 devices?

 

[guletz]

Hi,

If you have a mirror ssd I would not use zvol. I would create one big file on ssd pool and I use this file as special device(vdev). Performance will be better.

The best way will be to have a separate mirror for pmx and another mirror for special devices. I use consumer ssd for pmx only for at least 3 years for pmx device. In a case of broken OS proxmox I can reinstall the server in 20 min, and then import the zfs pool. During this time I can run my VM/CT on another node ....

Good luck / Bafta !

 

[ray.]

Ok, thank you, I think, I should test both.
Which size is needed for the special device for the raidz zpool with four 8TB (netto 24TB) hdds?
I have heard about 0.3%, but that seems to be too general, since pbs uses many small (<=4MB) files. Is 200GB large enough?

 

[guletz]

I have heard about 0.3%, but that seems to be too general, since pbs uses many small (<=4MB) files. Is 200GB large enough?

I read the same info.

Good luck / Bafta !