Do L2ARC cache SSDs have to be the same size?

[KevinM]

I've been looking around but I haven't seen a definitive answer one way or the other. What's the verdict?

 

[danb35]

The same size as what?

 

[KevinM]

The same size as what?

As each other. Say I have a 400gb drive and an 800gb drive. If I make them both L2ARC cache drives, do I end up with 800gb or 1200gb?

 

[danb35]

Unless you're planning on using them in a completely different system, you don't have enough RAM to effectively make use of L2ARC at all. But according to https://wiki.freebsd.org/ZFSTuningGuide, if you use more than one device, their capacities are added, so in the example you give, you'd have 1.2 TB of L2ARC.

 

[KevinM]

Unless you're planning on using them in a completely different system, you don't have enough RAM to effectively make use of L2ARC at all. But according to https://wiki.freebsd.org/ZFSTuningGuide, if you use more than one device, their capacities are added, so in the example you give, you'd have 1.2 TB of L2ARC.

Ah, excellent, thank you. I looked at a number of such guides but not that one.

The reason I asked, I picked up a couple of Supermicro 6048r-e1cr36l's and am using 8tb hgst nearline sas drives. They have 256 gb memory, 2 400gb p3700 nvme drives for zil and an 800gb p3700 for l2arc. I originally was going to go with 18 two way mirrors but caution got the better of me and I built the pool with 6x6 raidz2. Given the potential size of the working set, I'm thinking it might be better to break the mirror and grow the l2arc to 1.2tb. Now that I know it's possible, anyway.

I have a couple of 6047-e1r36n's as well (I replaced the raid cards with lsi hbas), also with 6x6 raidz2, and they've been problem free for several years now.

 

[cyberjock]

You do not have to have them all be the same size. In fact, I know *plenty* of people that mix and match them. ;)

 

[KevinM]

You do not have to have them all be the same size. In fact, I know *plenty* of people that mix and match them. ;)

Today I whacked the zil mirror and set one 400g p3700 as the zil, and used the second 400g and an 800g p3700 as the l2arc. That gives 1.2 tb, so about 4.7 times the 256 gb of memory in the box.

Thanks everyone for your help.