Disk drive selection, cache, and VM snapshots.

[VernMcGeorge]

A little background - I am moving from having separate bootable disk drives for different purposes (everyday use vs. financial vs. software development vs. games, etc. which has worked well in the past) to moving all of these systems into virtual machines because for some reason Windows 10 likes to make my disks unbootable and unrecoverable every now and then. So much easier to roll back to the last working snapshot.

 

Having watched several YouTube videos where multiple gamers are using one PC, I am interested in unRAID, but I have a couple questions.

 

Given that I have mostly SSDs should I just put all of them into the filesystem pool rather than cache? My reading so far indicates that the cache is only for write-caching and since my disks are all fast, there is no point.

 

Is there a way to create snapshots for VMs? If so, I have not found it. If not, could I just keep a backup copy of a VM under a different name?

[trurl]

SSDs in the array cannot be trimmed currently. Did you plan on having parity? If so more reasons to not have SSDs in the array. SSDs in the array would be slowed by parity updates, and it is possible that some SSD models could invalidate parity and so wouldn't really be suited for the parity array. Whether or not you have parity, you must have at least one data disk in the array.

 

The so-called "cache pool" is not only for write-caching, and most people keep some things on the cache pool permanently for performance and so array disks won't have to spin, such as dockers and VMs. And current beta allows for multiple fast pools which you can name as you choose, so they won't even be called cache.

[testdasi]

37 minutes ago, VernMcGeorge said:

A little background - I am moving from having separate bootable disk drives for different purposes (everyday use vs. financial vs. software development vs. games, etc. which has worked well in the past) to moving all of these systems into virtual machines because for some reason Windows 10 likes to make my disks unbootable and unrecoverable every now and then. So much easier to roll back to the last working snapshot.

 

Having watched several YouTube videos where multiple gamers are using one PC, I am interested in unRAID, but I have a couple questions.

 

Given that I have mostly SSDs should I just put all of them into the filesystem pool rather than cache? My reading so far indicates that the cache is only for write-caching and since my disks are all fast, there is no point.

 

Is there a way to create snapshots for VMs? If so, I have not found it. If not, could I just keep a backup copy of a VM under a different name?

A bit pedantic but Unraid has 2 concepts that you sort of mixed up.

• The "array" is basically data aggregation (like linux unionfs / mergerfs or windows DrivePool) with additional parity logic built on top. That's probably what you refered to as "filesystem pool". No trim on array and write speed is limited with potential (albeit rare) parity errors with SSDs. No RAID but allow mixed size drives (as long as parity is the largest).
• The "pool" aka "cache pool" or with 6.9.0 "fast pools" is basically RAID pool. It used to be used exclusively as write cache but that is archaic. The pool is basically used for anything that you want speed. It uses btrfs RAID (or optionally xfs for single-drive pool) so it restricts the sort of mixed-size drives you can use (e.g. 1TB+1TB+2TB RAID-1 is fine but RAID-0 will "lose" 1TB capacity).

There must be at least 1 device in the array. To run everything in the pool, some have had success with putting a spare USB stick (i.e DIFFERENT from the Unraid boot stick) in the array just to get over the requirement.

 

With SSD's, you are probably better off with them in the pool (and with 6.9.0, currently in beta, you can even have multiple pools).

I recommend you to either use 6.9.0-beta25 or wait till 6.9.0-rc1 (or wait till 6.9.0 stable, which has some way to go) as it works better with SSD's (mainly reducing excessive write and improving performance).

 

Snapshots, there are 2 main ways to do it, both not built-in.

• BTRFS can do snapshot natively. You can refer to the topic below with some sample scripts and methodologies by our btrfs guru johnnie.black. No 3rd-party software needed.
• Use ZFS snapshot - I use this for my 2 less important VM's. (My most important VM has all the NVMe's passed through for best performance). Need ZFS, which is a 3rd-party piece of software, which you need to install either with the ZFS plugin or use a custom-built kernel with ZFS already baked in (e.g. ICH777)

 

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