ZFS Special Device

[jfenning]

Has anyone tried using a ZFS special device to speed up the metadata on a ZFS HDD array? I run (24) 2.5 10k sas drives on hw raid. Performace is good thou my verify jobs take a very long time. I'm working on my next hw refresh. To test I'd have to blast my second PBS server and I was hoping to avoid that if someone has tried it.

 

[aaron]

Verify jobs will benefit a bit from a special device, but since it needs to read all data, not that much. GC will benefit quite a bit as it mostly only needs to access metadata.

If you add the special device later to your pool, only new data written will make use of it. You could probably force a new write of the data by doing a send/recv within the same pool. If you do have the space available.

 

[jfenning]

Thanks for the info. I decided the only way to know is to change my setup from hwraid to ZFS. I've got the controller so it an easy change over. Having some nvme enterprise modules sitting on the shelf helps. I'll leave my secondary hw raid so I can compare.

 

[itNGO]

I can confirm that the ZFS-Special-Device has improved performance for our PBS a lot.
We started with Logs and Cache-Devices and added Special-Device later. It has improved Garbagecollection by 50%..... took 2 days before and now finishes in about 16 Hours....