cache only setting

[wayner]

My appdata volume, and a few other volumes, are set to use the cache with the only setting. Do these volumes ever get backed up to the main data drives or are they only on the cache?

If they don't get backed up then is only the right setting or should I set up some sort of daily backup process?

Or should I be using an option other than only?

[Fuzzy]

cache drive is not backed up to the pool. You can either run your own backup process for it, or you can install a second cache drive that unRAID will backup the data with.

[stuckless]

Originally Posted by wayner

My appdata volume, and a few other volumes, are set to use the cache with the only setting. Do these volumes ever get backed up to the main data drives or are they only on the cache?

If they don't get backed up then is only the right setting or should I set up some sort of daily backup process?

Or should I be using an option other than only?

The Community Applications plugin (assuming you have it installed) contains a simple backup tool for doing automated backups of the appdata data to the pool.

[wayner]

I do have CA set up so I will install that. But just to ensure - Only is the best setting for the appdata drive rather than Yes or Prefer? I want to ensure the system is as fast as possible.

Why isn't there a built-in option for Only but Backup?

[Fuzzy]

Originally Posted by wayner

I do have CA set up so I will install that. But just to ensure - Only is the best setting for the appdata drive rather than Yes or Prefer? I want to ensure the system is as fast as possible.

Why isn't there a built-in option for Only but Backup?

If your cache is faster at random access, like an SSD, then yes, cache only would be the best option. They do not duplicate data between cache and pool because writing to the pool along with the cache would eliminate the purpose of the cache. If you want cache redundancy, you really should just add a redundant cache drive.

[wayner]

My cache is an SSD but it seems the way that the cache drive is being used is reallly a misnomer as, unless I am misunderstanding things, then it really isn't caching anything. Having another SSD as a backup cache is kind of a waste as I don't need the speed on the cache backup, just the redundancy.

[Fuzzy]

Keep in mind, everything in unRAID is built around the pool. The cache drive is there to compensate for the downside of the pool; that downside is the write speed, because of the parity writing needed. The 'caching' the cache drive is typically used for, is to take the data written 'to' the pool, and it is then transferred to the pool at the pools slower speed by the 'mover' process, which runs on a schedule. For the appdata and such, we are utilizing the cache drive simply because it is there, and for speed - there is nothing saying it HAS to be used, it's just that it is typically the fastest drive in an unRAID server, so it is the default location. Sage makes a very many small reads and writes, and years ago we noticed huge improvements moving sage to an SSD, even the much slower ones of that age.

If you are concerned about backing up the appdata folder, the three options were presented to you. The community sourced cache backup plugin that will make a copy on the pool in case you need to restore it; setting appdata's cache setting to yes or no, so it ultimately gets stored on the pool; or installing an additional cache drive so it has a redundancy at the cache level.

[Fuzzy]

I do not currently have a cache pool, because I got incredibly lucky with my SSD purchase (a ridiculously good D2RSTK251E19-0400 for only $80) that I will never be able to find for that price again to give it a twin, and anything else near that price will slow down the cache considerably (this thing reads at 560 MB/sec, and writes at about 400 MB/sec).

THIS shows why sage will run so much better on a high speed cache. This is a test I just ran on my unRAID server (this is read speeds)

[wayner]

Originally Posted by stuckless

The Community Applications plugin (assuming you have it installed) contains a simple backup tool for doing automated backups of the appdata data to the pool.

Thanks - I see that now. It appears that it stops your dockers while doing the backups so I guess you have to be careful with this with SageTV so that you don't interrupt any recordings.

[stuckless]

Originally Posted by wayner

Thanks - I see that now. It appears that it stops your dockers while doing the backups so I guess you have to be careful with this with SageTV so that you don't interrupt any recordings.

Yeah, I forgot about that (I don't use it myself).... That was a deterrent for me