Question about cache

[Meowcat285]

Hi, I was wondering if when files are cached, is there a copy of them stored on the array? If not, is there a option to enable that?

[hugenbdd]

24 minutes ago, Meowcat285 said:

Hi, I was wondering if when files are cached, is there a copy of them stored on the array? If not, is there a option to enable that?

No, there is only 1 copy of the file.  i.e. Cache Only

File is not on the array until mover sends it there.  If using cache-prefer it will copy files off the array to the cache drive.  However, if doing this on "media" shares, it can quickly consume all the cache drive and cause problems. (Very common to have problems with this setting.)

 

Best bet is to have your cache in a dual drive (raid 1) setup (i.e. mirror).  Mirror provides a backup of the cache drive, and parity protection will come once moved.  You can run mover every hour if needed.

 

There are some advanced users that have written their own scripts which will copy files back and forth from the array & cache drives.  However, it's not supported or recommended.

 

What is your use case for having copies on the array and cache?

[ChatNoir]

6 hours ago, hugenbdd said:

If using cache-prefer it will copy files off the array to the cache drive. 

Just to be very clear, the file will be moved, not copied with the regular Unraid behavior.

[Meowcat285]

16 hours ago, hugenbdd said:

No, there is only 1 copy of the file.  i.e. Cache Only

File is not on the array until mover sends it there.  If using cache-prefer it will copy files off the array to the cache drive.  However, if doing this on "media" shares, it can quickly consume all the cache drive and cause problems. (Very common to have problems with this setting.)

 

Best bet is to have your cache in a dual drive (raid 1) setup (i.e. mirror).  Mirror provides a backup of the cache drive, and parity protection will come once moved.  You can run mover every hour if needed.

 

There are some advanced users that have written their own scripts which will copy files back and forth from the array & cache drives.  However, it's not supported or recommended.

 

What is your use case for having copies on the array and cache?

I am using a older but still somewhat decent SSD, I am just a little worried about the drive failing, and I dont have another SSD I can use for cache, as my case doesnt have any more SATA ports.

[hugenbdd]

32 minutes ago, Meowcat285 said:

I am using a older but still somewhat decent SSD, I am just a little worried about the drive failing, and I dont have another SSD I can use for cache, as my case doesnt have any more SATA ports.

If you can't mirror the drive, and still want the "write" benefits of having cache, I would suggest a few things.

1.) Set mover to run hourly. (might need Mover Tuning to do this)

2.) Setup Squid's CA Backup's to backup all your dockers/plug-in's etc. to a share that does not use cache.

 

[trurl]

First thing to realize is that parity is not a backup. You must always have another copy of everything important and irreplaceable, on another system, even if the files are in the parity array.

 

And anything you intend to keep on cache that is "important and irreplaceable" must have backups also, even if your cache is a redundant pool.

 

Some things are less important or maybe not irreplaceable with a little work. Many things you might keep on cache are probably like this.

 

What do you expect to have on cache that is important enough to backup?

[Meowcat285]

4 hours ago, trurl said:

First thing to realize is that parity is not a backup. You must always have another copy of everything important and irreplaceable, on another system, even if the files are in the parity array.

 

And anything you intend to keep on cache that is "important and irreplaceable" must have backups also, even if your cache is a redundant pool.

 

Some things are less important or maybe not irreplaceable with a little work. Many things you might keep on cache are probably like this.

 

What do you expect to have on cache that is important enough to backup?

I was just wondering, it wasnt too much of a wory

[trurl]

4 hours ago, Meowcat285 said:

I was just wondering, it wasnt too much of a wory

 

 

This is a good idea and I do it and recommend it. Even more important is flash backup.

 

9 hours ago, hugenbdd said:

2.) Setup Squid's CA Backup's to backup all your dockers/plug-in's etc. to a share that does not use cache.