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whiteatom

"Back-up" option for cache only share

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I would like to see a "back-up" option added to the "use cache disk" option in the Share form. The behaviour would be to leave the data on the cache (like the "only" option) except the mover script would copy the data to the array when it runs.

 

My use case is my app data share for all my dockers. It's cache only now and working great, but I want it backed up to the array (so the pref files are on protected storage). When I asked about doing this, I was told to set up an rsycn cron job; but why does unRAID support moving through the webUI, but not copying?

 

Thoughts?

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7 hours ago, whiteatom said:

why does unRAID support moving through the webUI, but not copying?

Because if a file exists with the same name and full path on 2 different disks, only the first encountered file will be shown and modified in the user share file system.

/mnt/cache/share/file.foo gets moved to /mnt/disk1/share/file.foo -> only one instance of file.foo exists for /mnt/user/share/file.foo, so no conflict.

/mnt/cache/share/file.foo gets copied to /mnt/disk1/share/file.foo -> now /mnt/user/share/file.foo has to point to only one of the files, so the extra copy is hidden from view, causing operator confusion and other issues.

 

If you want to backup your files, use CA appdata backup plugin.

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As jonathanm said.

 

FIles and folders on cache are part of user shares so having them both on cache and array means you have duplicate file paths with no way for user shares to access both.

 

Many (most) people have the "use case" you mention so the CA Backup plugin was created. It creates the backup you are asking for on the array, but not in the same place mover would have put it, so it is not a duplicated path.

 

Have you tried CA Backup?

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No.. I found the CA plugin to be a total mess, so I gave up on it. That was a few years ago, so maybe i'll give it another try. 

 

I don't really see an issue with the user/share version of the files being hidden as you state. The cache version is the "live" version so that's they one we want - the other copy is just for redundancy.

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It's not the user share version that's hidden, both versions are in the user share because cache is also part of the user shares. If you have an appdata folder on cache, and an appdata folder on an array disk, both of those are included in /mnt/user/appdata. So it's unclear which version of the files /mnt/user/appdata would refer to. You are assuming that it is the version on cache that would get used but I don't know if that's true.

 

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There should be a way to mirror the cache drive to the data array for redundancy.  Or allow a mirror between a SSD cache drive and a disk drive.  Wait is that already possible or does it slow down the SSD drive reads / writes?

 

And why can't these data moves from cache to array be done with a background process instead of a scheduler at night?  I believe a RAID controller works this way, you write to the RAID cache (memory) and then the Controller moves it to disk as soon as possible.

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5 minutes ago, SonWon said:

There should be a way to mirror the cache drive to the data array for redundancy.  Or allow a mirror between a SSD cache drive and a disk drive.  Wait is that already possible or does it slow down the SSD drive reads / writes?

 

And why can't these data moves from cache to array be done with a background process instead of a scheduler at night?  I believe a RAID controller works this way, you write to the RAID cache (memory) and then the Controller moves it to disk as soon as possible.

Do you know how Unraid uses parity and how it uses cache? Take a look at this "Network Attached Storage" Overview in the wiki:

 

https://wiki.unraid.net/UnRAID_6/Overview#Network_Attached_Storage

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To clarify, I would like to setup the SSD cache drive to work like a HD disk cache, files accessed most often are read / write from the SSD cache avoiding accessing the slower array drives.  I think this was also the intention of the original post although he will have to speak up there.  This somehow drifted into a duplicate file location issue.  Where the real request, at least from me would be for the cache to be a cache where the most often used files are also stored on the cache for quick reads / writes.

 

The SSD cache is currently only a write cache, there is no read cache going on from what I've read so far.  This is a unneeded limitation from a technology prospective.

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Put together the info at that link with the details of how disks actually work and it does answer your questions. Things can only go so fast.

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Just now, trurl said:

Put together the info at that link with the details of how disks actually work and it does answer your questions. Things can only go so fast.

Did my second post change your answer?

Edited by SonWon

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You can have a user share set to stay on cache and you can have a redundant cache pool. These features are already in Unraid and no need to get the array involved.

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Just now, trurl said:

You can have a user share set to stay on cache and you can have a redundant cache pool.

Yes, I know, those are not the features being asked for.  I must not be explaining myself well.

 

A user share on the SSD cache doesn't get stored to the array so it isn't being cached just stored on a different drive.  Unless that isn't correct but everything I've read leads me to that understanding.  If my understanding is correct then this is only a write cache.

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There is nothing that tries to predict which files you want faster access to and automatically moves them to cache if that's what you mean. Unraid gives you the means to manage these things yourself while keeping things simple and reliable.

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I get that which is why my post was here in Feature Request.  As I believe it would be a nice feature to add and make unRaid even more useful.  I didn't expect this push back in the Feature Request forum?  I get that some features are difficult to implement.  I've also been around software developers too and understand sometimes they just say no because they don't see the need.  This would also push unRAID up another level.

 

Anyway, thank you for your replies and I will hope this gets serious consideration one day.

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