TrueNAS Mini XL+ w/ SLOG & L2ARC?

[TrueNASty]

Hi,

I've got a:

1) TrueNAS Mini XL+ Compact ZFS Storage Server with 8 + 1 Drive Bays, 32GB RAM, Eight Core CPU, Dual 1/10 Gigabit Network
2) 8x WD Red 10 TB drives
3) TrueNAS Mini 480GB Read Cache (L2ARC) Upgrade
4) iXsystems TrueNAS Mini Write Cache (ZIL) Upgrade

Regarding 3 & 4, I bought from these links respectively:

https://www.amazon.com/dp/B08FCW8VND/

https://www.amazon.com/dp/B08FCWK8B9/

I'm not sure that why they're marketed differently because when I got them, they appear to be identical: two 480GB SSDs.

Anyway, I installed the two SSDs internally on the two available bay areas and I filled up the 8 3.5" hotswappable bays with the WD Red 10 TB drives. I may add a 1TB SSD to the top hot swappable bay at some point.

When I went to configure the two SSDs as L2ARC and SLOG drives, I got confused, so I had a little discussion with ChatGPT and this is what it recommended I do:

Partition two SSDs, allocating 32GB on each for SLOG and using the remaining space for L2ARC. The SLOG partitions will be mirrored between the two SSDs, while L2ARC will be set up without mirroring.

I tried to partition the SSDs from the shell to no avail. Does this seem like a good setup? Or should I try something else?

Thanks,
TrueNASty

 

[TrueNASty]

Also, I'm running TrueNAS-13.0-U5.3 CORE.

 

[somethingweird]

you should at least max out RAM before you start with L2ARC.

At what point does l2arc make sense

At what point does L2ARC make sense?

The default advice here is "max out RAM, then add an L2ARC if needed." When I built my recent test machine that's exactly what I did, so no L2ARC was added even though I've got 72 gigs of ECC RAM. But now I'm looking around and seeing machines with 64G of RAM and significant L2ARCs, and I'm...

www.truenas.com

 

[Davvo]

I'm not sure that why they're marketed differently because when I got them, they appear to be identical: two 480GB SSDs.

From one review it appears the ""write cache"" one (SLOG, which is not exactly a write cache) should be overprovisioned and appear as a 16GB drive. Maybe iX Staff can tell you more.

When I went to configure the two SSDs as L2ARC and SLOG drives, I got confused, so I had a little discussion with ChatGPT and this is what it recommended I do:

Partition two SSDs, allocating 32GB on each for SLOG and using the remaining space for L2ARC. The SLOG partitions will be mirrored between the two SSDs, while L2ARC will be set up without mirroring.

Do not use ChatGPT!! It's NOT a reliable source!!

Public Service Announcement: Do NOT rely on ChatGPT's <sarc>advice</sarc> on fixing or configuring TrueNAS

This is because ChatGPT will happily make stuff up in such a manner that sounds plausible, but is fundamentally GIGO (Garbage In - Garbage Out).

www.truenas.com

Completely trash what it has told you: you shouldn't do any partitioning using TN, and you should NEVER use a single drive for different purposes, especially a SLOG!

Some insights into SLOG/ZIL with ZFS on FreeNAS

What is the ZIL? POSIX provides a facility for the system or an application to make sure that data requested to be written is actually committed to stable storage: a synchronous write request. Upon completion of a sync write request, the underlying filesystem is supposed to guarantee that a...

www.truenas.com

As others said, you should have at least 64GB of RAM in order to consider L2ARC.

The proceudre is simple: from the WebUI add another vdev to the pool you want, then select CACHE (for L2ARC) or LOG (for SLOG).

/core/uireference/storage/pools/

EDIT: RED drives (without PLUS or PRO) are SMR, which is NOT compatibile with ZFS!

 

[TrueNASty]

Currently using CORE.

 

[Davvo]

Currently using CORE.

Updated the post with the correct configuration procedure.

 

[Ericloewe]

As others said, you should have at least 64GB of RAM in order to consider a SLOG.

Not really, the need for SLOG is essentially independent of system memory. An SLOG is necessary if the in-pool ZIL cannot keep up with the required performance and disabling sync is unacceptable.

 

[Davvo]

Not really, the need for SLOG is essentially independent of system memory. An SLOG is necessary if the in-pool ZIL cannot keep up with the required performance and disabling sync is unacceptable.

Absolutely, I wrote SLOG instead of L2ARC. Thank you for pointing it out, editing immediately.

 

[HoneyBadger]

From one review it appears the ""write cache"" one (SLOG, which is not exactly a write cache) should be overprovisioned and appear as a 16GB drive. Maybe iX Staff can tell you more.

Correct; the "write cache" SSD should be overprovisioned and show up in your system as a 16GiB unit.

@TrueNASty do both of your SSDs show up as 480GiB in the UI? If your write log wasn't set to 16GiB from the factory, you can do this either from a GUI setting or the shell by following the tutorial here (for CORE):

SLOG Overprovisioning

Describes how to configure SLOG over-provisioning on TrueNAS CORE.

www.truenas.com

Unfortunately ChatGPT is not accurate when it comes to recommending technical information or how-to's for TrueNAS.

 

[TrueNASty]

Based on what you folks are saying it sounds like I'd be better off putting these SDDs into a mirror and using them for Virtual Machines or whatnot.

 

[TrueNASty]

I'm thinking about upgrading to 64GB of RAM so I can run a few Virtual Machines on the NAS.

https://www.amazon.com/TrueNAS-Mini-XL-Upgrade-Registered/dp/B08FSN61C3

A few of you have said that if I go up to 64GB of RAM, that might justify using these SSDs as either a L2ARC or SLOG. Perhaps both, although if I'm just using 16GB of SSD for SLOG on one drive it seems like a waste of space.

 

[TrueNASty]

Correct; the "write cache" SSD should be overprovisioned and show up in your system as a 16GiB unit.

@TrueNASty do both of your SSDs show up as 480GiB in the UI? If your write log wasn't set to 16GiB from the factory, you can do this either from a GUI setting or the shell by following the tutorial here (for CORE):

SLOG Overprovisioning

Describes how to configure SLOG over-provisioning on TrueNAS CORE.

www.truenas.com

Unfortunately ChatGPT is not accurate when it comes to recommending technical information or how-to's for TrueNAS.

Yeah, both drives show up as 480GiB in the UI under Storage > Disks.

I put them in a pool temporarily but I haven't really used them for anything yet. I can always delete it and use them for something else if you guys think it makes better sense.

Regarding overprovisioning, these are my current settings:

 

[Davvo]

SLOG is not influenced by RAM, it is used alongside VMs/block storage; L2ARC requires at least 64GB of RAM in order to justify its usage.
Just to make things clear since I miswrote and conseguently edited this part in my previous post.

 

[Etorix]

SLOG is for sync writes. No sync writes, no SLOG, irrespective of RAM. Over-provisioning is for resiliency, since SLOG duty is write heavy (and mostly write only).

With respect to L2ARC, you need sizeable RAM before even considering L2ARC, but more RAM means you're less likely to benefit from L2ARC.

It's quite possible you don't need either and that the drives may be repurposed as a fast mirror pool for apps/jails/VMs.

 

[HoneyBadger]

Yeah, both drives show up as 480GiB in the UI under Storage > Disks.

View attachment 71194

I put them in a pool temporarily but I haven't really used them for anything yet. I can always delete it and use them for something else if you guys think it makes better sense.

Regarding overprovisioning, these are my current settings:

View attachment 71195

If the VMs you're using will fit entirely into the 480G size limit of your SSD pool, that's definitely the easiest solution. If you did want to set up cache/log then set the "log overprovision size" to 16G in the settings option before adding it.