Adding SSD cache to existing SATA ZFS pool

[255044]

Hi all,

I have a dell poweredge with 3X 1tb SATA drives in 1 ZFS pool.

state: ONLINE
scan: none requested
config:

NAME STATE READ WRITE CKSUM
rpool ONLINE 0 0 0
raidz1-0 ONLINE 0 0 0
ata-ST1000NM0018-2F2130_ZFA129QQ-part3 ONLINE 0 0 0
ata-ST1000NM0018-2F2130_ZFA11K5S-part3 ONLINE 0 0 0
ata-ST1000NM0018-2F2130_ZFA129M6-part3 ONLINE 0 0 0

This one pool has my pve install on it and my windows 2019 vm

I have one additional zfs drive (4tb) whcih is used for windows backups but want this to remain separate.

I now have my hands on a dell server SSD and i would like to add it as a cache to speed things up

Can someone please tell me how i go about adding this in?

thanks

 

[SergeyMorozov]

zpoll add rpool cache <your-ssd-drive>

 

[Dunuin]

First of all you need to know what you want to do with it.

1.) L2ARC = read cache. Will only be used if your ARC is full because it makes your HDDs slower if used, because using the ARC in RAM would be faster. So if you got enough RAM a L2ARC is useless. And if your RAM is too small it would be better to install more RAM. So L2ARC is only usefull if you already maxed out your RAM and can't add more.

2.) SLOG/ZIL = write cache. Will only be used on sync writes and NOT on async writes. And because in most cases nearly only async writes will be used a SLOG is in most cases quite useless.

3.) "special device". SSD will be used to store metadata and small files that would go otherwise on the HDDs. But this isn't a cache. Some data will be stored on HDDs and some on the SSD.

Also keep in mind that you might loose all the data on your HDDs if the SLOG/special device dies and is not mirrored.