Hi Guys-

I tried to hunt for the answer, but did not seem to find anything definitive.

What exactly does cache disk support do / achieve?

I'm trying to figure out with my pending upgrade if I would be better served adding a new drive for more overall storage capacity or 'sacrificing' that disk as a cache drive.

The cache drive is used as a temporary place to hold a file you copy from your PC to the unRAID server.  It is not part of the array protected from failure.  Since parity does not have to be calculated when a file is copied to it (since parity is not calculated) the speed of "writes" to the unRAID server is faster.

 

When the cache drive is installed and configured, you simply use your array as you always have.  When you copy a file from your PC to the unRAID server it is initially saved to the cache drive.  At periodic intervals, the unRAID server moves the file from the cache drive to the data drive it is assisting.  Until the file is moved, it is not protected from a drive failure.

 

 

The cache drive does not need to be as big as your data drives.  It does need to be big enough to hold all the files you might transfer at a given time. ( between its scheduled interval to copy its files to the data disks)  It would be a perfect place for the old "small" 40 Gig drive you might have laying around if all you do is copy a few files per day to the unRAID server.

 

Benefits:

You gain speed in writing to the unRAID array. 

Drawbacks:

You give up parity protection until the file is moved by the unRAID server from the temporary cache drive to the data drive. At that point it is protected.

 

Joe L.

 

Is the cache drive facility part of unRAID PRO or is it available on other versions too ?

 

 

The cache drive was introduced in Release 4.3-beaa4 and is described in the release notes here:

http://lime-technology.com/forum/index.php?topic=1731.msg11937#msg11937

 

It is only available on Pro Licenses.

 

Joe L.

Other than enabling it in the Shares "Use Cache Disk" = Yes,

Is there anything else you have to do , like create the directories?

Cach disk is generally for user shares.  Without user shares, you have to move files manually.

 

I started working on a monitoring process, that let you create directories on the cache disk:

 

/disk1
/disk2
/disk3
...

 

The process would scan these dirs periodically, and if a file existed on the cache and not the /mnt/diskx, it would make a symlink to the cache disk.  Then at night, a mover script would move them to the final destination.