SSD as cache drive


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Are any precautions needed when using a SSD as a cache and app drive regarding garbage collection?

Is it wise to use it as SABNZB download/verify/repair and unpack station? Or would it be wiser to do the unpacking straight to the array (I.e. set mnt/user0 in SAB as completed download folder. so the SSD doesn't fill up)? I set the final folder in categories.

Which SSD would be best suited for this task? Pricewise 256 GB will be the max.

 

Maybe it is wiser to use a spinner? Maybe a hybrid laptop drive?

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Another way to do it is format an SSD ext4 and manually mount (or use SNAP).  You would also have to setup your own mover script if you use as a cache drive.

 

I've done this for a SABNZB/App drive (not with SSD, but wanted to be able to have unRAID shutdown cleanly without worrying about shutting down applications that have a file lock on the array).

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Another way to do it is format an SSD ext4 and manually mount (or use SNAP).  You would also have to setup your own mover script if you use as a cache drive.

 

I've done this for a SABNZB/App drive (not with SSD, but wanted to be able to have unRAID shutdown cleanly without worrying about shutting down applications that have a file lock on the array).

 

Sure is a nice option, but too complicated for a Linux noob like me :). 3 problems at least:

How do you mount such a drive permanently, also after a reboot? You just add the mount command to the go script? And how to format such a disk to ext4?

How to write a mover script?

 

Sure would be a nice experiment. I could start small on my test server.

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The only reason I see to use an SSD on a cache drive for something like this would be the supposed savings in power or speed (but mostly power)

Do you want the added complexity and cost to save some power?

 

For me, SSD in cache makes sense since I use it for apps and as an NFS mount for all my /home directories.

For me, I do not want the wait time for spin up and spin down. I need it active all the time.

 

For a torrent downloader drive, I would choose a magnetic spinner unless I wanted to save power as much as possible.

Maybe calculating KWH cost vs cost of SSD would show where the saving begins.

Then you have to calculate the average lifetime of the SSD.

 

I usually recommend a cache drive as large and fast as parity.

This way if any drive fails in your system, you could sacrifice your cache drive to replace the failed drive while getting a replacement.

 

Now if you are like me with the hybrid RAID0/RAID1 setup, the SSD may be more effective since there will not be competition with the parity drive.

In this case, performance does matter and it's greater then the cost of the SSD.

 

Now about those questions. I'm not even sure that unRAID supports EXT4 yet.

Mounting... if it's your cache drive, unRAID will handle the mounting.

If it's not, then you can mount it in your go script pretty easily.

 

 

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Thanks Weebo, you give me some things to think about. Like you I use the Areca RAID1/RAID0 setup as parity/cache. For now I just gonna stay with that setup. Just had a crazy idea and saw some slowdown when downloading with SABNZB. Had totally forgotten that the mover was running copying data from cache to array, SABNZB was downloading and Parity check was running. I guess the Areca 1200 was sweating together with the 2 attached disks! When the mover finished overall speed went up.

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