Good day,
Reading hours on end on what to do and what not to do there are some consideration that I would like to run past the more veteran Truenas users.
TL:DR;
Can I use a mirrored drive as SLOG and Special Metadata Device?
If no: Using a single drive for Special Metadata Device recommended?
Is there any consideration I need to take into account for USB SSD boot device?
The setup:
Intel 12th Gen 1235U
64GB RAM
A2000 ADA
4 x NVMe Gen 4 x 4
1 x NVMe Gen 3 x 8
6 x SATA 3.5 bays
10GbE
For now I think I would only be using 2 pools
Z1 pool with 3 x NVMe 4TB drives
Z1 pool with 6 x HDDs 24TB drives
That leaves me with 2 NVMe drives left. The initial intention was to use 2 drives in mirror for the OS and use a partition for SLOG. This seems only possible if I partition the drive which is not recommended for the bootdrive. Instead I would load TrueNAS from an USB SSD and have a mirrored setup usable for SLOG and special metadata. I intend to use 2 x Optane P1600X 118GB
The first question then pops up:
Can you use the same drive/mirror for SLOG and Special Metadata? - if yes: GREAT! We are done.
If I cant use the same device for SLOG/SMD(Special Metadata Device), is a single drive for SMD fine for home use? I am a bit worried about this as it can break the pool if itâs lost. SLOG and L2Arc are not as critical.
For the bootdrive I would like to use an internal USB connection, I understand a regular USB is going to wear out very quickly, USB SSD however seem to provide enough endurance. What do I need to look out for?
All I then have to consider is L2Arc, do I need to plan for that with my prosumer needs? Seems to be used in certain setups but not for just media/docker images.
You can indeed (manually) partition drives and use them for all kinds of SLOGs, special metadata and L2ARCs. The OS will not assist you in this because itâs deeply discouraged.
Having said that, there are guides floating around in the ether that show you how to do it.
Some users are okay with this and nothing I or anyone else here say will likely change their mind. You will be on your own, that includes if you run into issues later.
A special note about special metadata is that once you add them, you canât remove them without remaking the pool. Because losing the special metadata VDEV is a total pool lost the recommendation is that the metadata VDEV has the same level of redundancy as the data VDEVs. That means a RAIDZ2 setup should use a 3-way special metadata mirror VDEV to support it, allowing for the loss of up to 2 devices in any individual VDEV without losing the pool.
By a) not having mirrored special metadata VDEVs and b) overloading the devices combining SLOG and special metadata on the same devices, you are adding a sizeable amount of risk.
I canât say if this is fine for home use because âhome useâ is not specific enough.
- Home use could mean that you will use them to store your YARR stack of pirated material, that youâre willing to spend time to redownload if everything goes up in flames.
- It could also mean that you plan to store your familyâs photo and video history over the past 40 years. Something you canât just recreate (barring secret time machine).
- It depends on your backup regimen, do you adhere to a 3-2-1 backup strategy or equivalent?
- How long can you withstand downtime and what is your time that you need to spend fixing it worth to you?
All of this feeds into how risk averse you should be and in the end, that is something only you will know.
Finishing up, I would say that you likely donât need any of those non-data VDEVs.
- A SLOG will only help if your clients use sync writes, chances are none of your clients at home do.
- Special metadata has a use case if you store many small files and load times are essential. Considering the added risks and complexity, I personally donât think itâs worth it for most home users. This device is pool critical.
- L2ARC can help if you find yourself needing faster access to frequently used data (as in, you access the same data over and over). There are layers of complexity here that mean that you should only consider L2ARC if you have plenty of RAM already, and that you see arc misses.
- Thereâs also DEDUP VDEVs, another type of pool critical device. Iâll keep this short and just say: Just donât. Donât use a DEDUP VDEVs.
Edit: Perhaps unexpectedly, if you have a backup of your config-file (and you should) you likely wonât benefit much from having a mirrored OS drive. Reinstalling anew and restoring your backup config is such a trivial thing that it is what I recommend most people do instead.
Adding to this: depending on how the boot manager set things up you may not be able to reboot as normal if one OS drive has failed without tinkering a bit.
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Home use in this case would mean media-apps, password managers, mail bridges and vpn clients for a few users. Nothing is truly mission critical as the application for the nas is just for leisure.
I will take your advise to use backups of the config instead of mirroring the OS drive. It makes more sense and it fits perfectly with the use case. Any notable brands or models of USB SSD drives you can recommend?
What I am still unclear about is if I can assign the same mirror for SLOG and special metadata vdevs, you describe the risk associated with it. Can I assume that it is technically possible?
The other consideration would be mirror the special metadata vdev with the optane drives that have PLP and partition a portion for SLOG on the other nvme pool in z1 configuration?
Is it even possible to partition drives in a pool or should that be done before the pool is created?
Of the ones you mention I take it you have backups of your passwords and mail, as I can see those being rather important, depending on how you use them.
USB is somewhat less reliable than SATA and the like. I have seen cases being made that itâs good enough for boot drives as long as weâre talking proper SSDs, not USB flash drives.
I use neither myself and canât offer any recommendations.
Yes, this is possible. You can have a SLOG/Special metadata/L2ARC/DEDUP-partitoned chimera device if you really want to. You shouldnât, but you can.
My answer to this is the same as before. You can do that, you shouldnât. Itâs unsupported. It may work today and fail tomorrow. iXSystems does not test their software for this use case. Youâre of course free to tinker with it but understand the risks. A 2-way mirror + Z1 data VDEVs at least checks the equal redundancy box. The partitioning less so.
How you go about partitioning drives in this manner is something I will leave to the partition witch doctors to comment on.
You donât mention it in your initial post, but what motherboard do you plan to use? Most boards do not have that many NVMe slots. Are you going to use a PCIe card? Have you verified if it requires bifurcation or not and if your motherboard supports the required 4x4x4x4 set up (for example)?
Thank you for the insights neofusion. I will abandon the âchimeraâ vdev idea of having slog/special metadata on a single drive. I will create a mirror of Optanes and test whether my usecase benefits from non pool-critical solutions like L2Arc or SLOG first.
For boot I will make sure its a USB SSD and not a regular stick.
There is an add-in card that has PLX chip on it so I donât need bifurcation on the mobo.
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