Does SLOG / L2ARC / META disks make sense in this case?

TrueNAS General
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1

I’m in the process of migrating a ProxMox video editing / content backup server to TrueNas and have been looking into SLOG / L2ARC and Meta drives.

The hardware (Intel i7, 64gb RAM) has three “layers” of storage:

  1. layer is fast storage (a number of NVMEs on the board) for day to day work / offloading of footage / editing / export of files
  2. layer is medium fast (a number of SATA SSDs) for content library when a project is done
  3. layer is slow (a number of HDDs) for daily backups og layer 1 and 2

As I understand it, SLOG / L2ARC / META disks can be added to improve speeds but in this case, I would like to know if this is actually a benefit in our case or if it will just complicate things.

I get that SLOG / L2ARC / META disks reduces the bottleneck in “pure” HDD setups because the HDDs are slow - but in case of NVMEs and SSDs, I’d really like to make sure that I understand if and how/why SLOG / L2ARC / META would bring noticeable improvements.

Thanks in advance to anyone sharing their thoughts on this - much appreciated :pray:

2

SLOG is only useful for sync writes, which you do not appear to have, and then maximal performance is always achieved with async and no SLOG.

A special vdev only makes sense if it is faster than the main storage. It wouldn’t make much sense for layers 1 and 2. Layer 3 being a backup, there’s no user benefit to speeding it.

As for L2ARC, use the system and test first. But, again, there’s the question whether there is a tangible benefit to speed up storage which is already fast.

3

This is what I did. I considered adding an NVMe as an L2ARC vdev to speed up metadata reads.

Before trying this, I doubled my RAM from 16 to 32 GiB and saw immediate benefits. I no longer consider using an L2ARC.

4

It comes down to what is faster, nvme (l2arc) or memory. Obviously, it’s memory. So, memory always better.

5

In this particular scenario, for the primary activities on layer 1 and 2, you seems to have already assigned faster mediums nvme/sata ssds. That sounds like a solid plan.

Now its not very clear what is the ratio between ssds v/s hdds. But from the info here my understanding is that the hdds are mainly used for backup. Also I believe as the content library grows it might have archived backups too. (For the clarification I refer as archived = content only existing in layer 3 and NOT in layer 1 or 2). Now if you would need to access some of the archived videos (like browse through, search for an older one etc.) having a META drive (special vdev), especially on nvme, will help a lot.

Also, in case you decide to go with the META drive, please ensure that a mirror is a must for meta drive. If possible I would suggest a 3 way mirror for meta drive, for the peace of mind.