Using SSDs as Unassigned Devices

[gambcl]

While I am waiting for my new system's hardware to arrive I am trying to sort out what configuration I will need.

 

I would like to separate my dockers,VMs and Plex database from my cache-pool.

 

As I understand it, I can setup two 1TB SSDs as a cache-pool and Unraid will automatically use BTRFS and give some kind of mirroring/RAID1 across the two SSDs for protection of the cache.

 

Then I can use the Unassigned Devices plugin to mount some extra SSDs to use for dockers,VMs and my Plex database.

My questions are around this area:

1) What is the best filesystem to use on SSDs used in this way? (i.e. NOT part of the array, only used as Unassigned Devices)
   Do I have to worry about TRIM?

 

2) Can I use pairs of SSDs for these Unassigned Devices and get the same kind of mirroring/RAID1 that the cache-pool gets?

 

3) Or is it better to just use a single SSD for dockers,VMs via Unassigned Devices, and then get that SSD backed up to the array overnight?

 

If I can do the mirroring for the Unassigned Devices then I would happily buy the extra SSDs for the protection, but if it just isn't possible then I can save some cash.

 

I have been reading the forum looking for this info but many of the posts were quite old, and talked of BTRFS corruption, etc. So I'm just looking for some up-to-date wisdom.

 

Thanks for any help,

 

Charlie
 

[tdallen]

FYI, you can put more than two devices in the cache pool.  The standard approach is either more devices in the cache pool or single devices backed up to the array.  Unassigned devices don't have redundancy unless you put them behind a hardware RAID controller like an Areca.

 

A disclaimer I've been making a lot recently - I think caching writes to the array is unnecessary most of the time.  You might want to think through what you are trying to accomplish, and what advantage you are trying to gain by write-caching.  If it turns out you don't really need it, those 1TB SSDs will have a lot more room for Dockers and VMs.

[gambcl]

44 minutes ago, tdallen said:

FYI, you can put more than two devices in the cache pool.  The standard approach is either more devices in the cache pool or single devices backed up to the array.  Unassigned devices don't have redundancy unless you put them behind a hardware RAID controller like an Areca.

 

A disclaimer I've been making a lot recently - I think caching writes to the array is unnecessary most of the time.  You might want to think through what you are trying to accomplish, and what advantage you are trying to gain by write-caching.  If it turns out you don't really need it, those 1TB SSDs will have a lot more room for Dockers and VMs.

 

Thanks, that's just what I was looking for, and answers 2 and 3 above.

I'll go with twin SSDs for the cache-pool and single disks for Unassigned Devices usage, backed up nightly.

 

I know there is a plugin for backing up to the array, can it handle multiple drive backups?

 

Any thoughts on filesystems for the single-disk SSDs?

I had thought that BTRFS was optimised for SSDs, but would XFS on the SSDs be more reliable?

 

 

[tdallen]

The main reason to use BTRFS right now is its RAID capabilities which don't apply to a single unassigned device.  UD supports a number of formats, I'd use XFS.  I don't have any persistently mounted UDs right now so I can't offer advice on the best way to schedule trims and backups.