iSCSI space usage when fully provisioned?

[nickwebha]

I have TrueNAS set up to serve iSCSI to my container server. The iSCSI volume is pre-allocated. Everything works great. I enabled Gzip and deduplication (yes, dedup is doing great).

Here is my question: Is any space actually saved by having compression and/or dedup on a pre-allocated volume? That seems logically counterintuitive.

I can not seem to find this answer.

 

[Samuel Tai]

You don't have enough RAM for dedup. You need at least 128 GB, with 512 GB preferred.

 

[nickwebha]

I mentioned the dedup to be clear. Dedup is not causing any problems or slow downs.

What I really want to know is what happens when you enable compression and/or dedup on a preallocated zvol. Assuming theses were zvols with compressible, does it acutally free up space I would not have otherwise had?

I am tired so I hope I am making myself clear.

 

[jgreco]

I mentioned the dedup to be clear. Dedup is not causing any problems or slow downs.

It will, in the long run. Once enabled, it really requires destruction of the pool to expunge the negative effects of dedup.

what happens when you enable compression and/or dedup on a preallocated zvol. Assuming theses were zvols with compressible, does it acutally free up space I would not have otherwise had?

No, it doesn't. Compression and dedup only affect newly written data.

Are you running iSCSI on a RAIDZ3? Don't.

Resource - The path to success for block storage

ZFS does two different things very well. One is storage of large sequentially-written files, such as archives, logs, or data files, where the file does not have the middle bits modified after creation. This is optimal for RAIDZ. It's what most...

www.truenas.com

 

[kspare]

Im running 1tb of ram, 22 mirrored 4tb drive, 12 800gb sas l2arc drives, mirrored slog, and mirrored special vdev.

We run terminal servers on this storage. at this point does it make sense to start looking at dedup to increase performance?

 

[jgreco]

Yes, quite possibly, but be aware of the difficulties. There's an article by Stilez in the Resources section that should be instructive. Also, be aware that iXsystems is currently seeking a sponsor for dedup improvements. Even if that sponsor isn't you, you need to be aware of the likely possibility that things will change in the near-ish future.