What if controller "dies"

TrueNAS General
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1

Hello,
I am planning to build truenas but i have hindering questions. What would happen if the controller dies, with RAID it is very hard maybe not even possible to recover drives, what what about truenas, so planning to plug in drives to sata on motherborad and question is if that mb dies then can i replace mb? Does order where cables are plug in are matter or not?

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As long as your drives are not affected, you can recover the pool. The issue usually is that a HBA failing will not happen in an instant and will cause trouble with the data… which ZFS should generally be able to handle.

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That’t the difference between a specific RAID controller and a HBA that solely reads/writes from disks.

If your RAID controller dies, you likely have to replace like for like. If you are unlucky, some data re: config are stored on the RAID card itself, making recovery that much more difficult, even if you have a SKU to SKU match for the RAID controller. Depending on the age of the controller, getting an exact match by SKU and firmware might be really difficult.

On the other hand, with ZFS, the pool data is stored in the config file. You can make backups of it. Disks are addressed by their UUID, not whatever addresses / abstractions the OS might come up with. With ZFS you can:

  1. Change the controller
  2. Switch / Swap SATA plugs around
  3. Change the motherboard / RAM / CPU / etc.
  4. Swap OS (i.e. TrueNAS Core to Scale, for example)

Next time you boot (assuming the BIOS is good, all electrical / logical connections are good, etc.), the ZFS pool should just come up. That is one major reason that a ZFS system, all things being equal, is superior to a hardware RAID approach (besides the upside of a Z2 or whatever vs. RAID 6 like scrubbing, replication, snapshots, and so on).

Unlike most RAID arrays, you can keep adding features and/or drives to a ZFS system, i.e. a sVDEV for small files and metadata, a L2ARC, or even additional VDEVs to expand capacity.

RAID cards certainly have their place but I’d question their use for anything

  1. at significant scale (i.e. more than 5 drives unless it’s for single-user, scratch use)
  2. that is supposed to be around for a long time (i.e. can deal with bit rot)
    Etc.

Given how well some RAID cards are built, even 1) and 2) are questionable at any scale (still bitter about that XFX RAID controller that silently corrupted much of my Mac G4 array, circa 1999). The ability of ZFS to detect issues with data being written badly, etc. is a game-changer vs. RAID.

ZFS is paranoid, regular RAID just traipses through life with a Alfred P Neuman “What me, worry?” outlook. If you value your data, it’s primary repository has to be something like ZFS.

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4

Slight correction here:

The ZFS pool configuration is stored INSIDE the pool. So any OS with compatible ZFS version can import the pool and make the data available.

However, the TrueNAS configuration with shares, App config, network config, etc is easy to download or E-Mail. You can even automatically save a copy to your ZFS pool.

What I mean by “compatible ZFS version” is that ZFS is under active development, (which is good), but, some new on-disk pool features are not compatible with older ZFS software. In many cases those “new on-disk pool features” can be left disabled making the pool more compatible with older ZFS software.

Thus, one recommendation in this forum is to NOT upgrade your ZFS pool feature(s) unless you really need one. Then perhaps only enable that specific feature, and not all new pool features.

PS @Constantin knows the difference I explain above, he likely just mis-wrote the answer.

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