Cache Drive question


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Hello,

 

I'm am just getting started using unRaid and have some questions about the Cache drive.  I was reading through the Wiki pages when I came across this last paragraph, which kind of spooked me: '

Amount of data

The final consideration in choosing a cache drive is to think about the amount of data you expect to pass through it. If you write ~10 GBs per day, then any drive 10 GB or larger will do (a 30 GB SSD may be a good fit in this case). If you write 100 GB in one day every few weeks, then you will want a cache drive that is larger than 100 GB. If you attempt a data transfer that is larger than the size of your cache drive, the transfer will fail.

 

I know this is a little outdated, but my concern it that I will be going from a video server that runs and stores my Plex media (1 to 1 BluRay rips) to a new tower running unRaid.  My library is running a little over 5TB in size and my concern is that if I try to copy all of that over and it's larger than the cache drive, will the copy fail and possibly lose what I'm copying over or will it just copy to the data pool and by-pass the cache drive? Thanks for any help.  I'm sure I'll have plenty more questions.

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Out of the box, mover will move files from the cache to the array at most once per day.  If you have say 20gb out of 100gb free at that point and you try to write a 30gb ffile depending on your mover settings the following will happen:

 

 

- 'cache only' - file too big so will fail

- 'prefer cache'/use cache'- file will get written to the array

 

There is a new cache plugin that allows you to run mover hourly at a set threshold e.g for my 500gb cache, I have set a 80% threshold so if at the hourly check point my cache is over 400gb full, the mover runs - if not it doesn't.

 

For my big shares like movies I've set a 60gb min space free rule, this means that my cache will always have the amount of space I need as my dl speed is slow.  If I had a faster download, I'd just lower my threshold e.g. 50% to account for more new data being written faster.

Edited by DZMM
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1 hour ago, John_M said:

It's called CA Mover Tuning. It's support page is here:

 

 

Thanks - i was at swimming with my daughter on my phone and couldn't remember the name (also why posted gb and not GB as I couldn't be bothered to switch to caps!)

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4 hours ago, craignan said:

My library is running a little over 5TB in size and my concern is that if I try to copy all of that over and it's larger than the cache drive, will the copy fail and possibly lose what I'm copying over or will it just copy to the data pool and by-pass the cache drive? Thanks for any help.  I'm sure I'll have plenty more questions.

If you're moving a lot of data in bulk I would just write it direct to the array (no point 'stressing' your cache pool if the files are going straight to the array) - if you turn on Turbo Write you should get  good speeds of over 100MB/s - 5TB should take less than a day to move over

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Thanks DZMM, that was going to be my next question.  I think that would be the best way of moving all of my data (Movies, TV Shows) without being worried about the cache drive. One last little question :D, the Turbo Write, is that a feature of unRaid? If it is, where do I enable that?  Currently running 6.5.0.

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Unless you set a User share to use cache, it won't since the default is cache-no. Each user share has settings that control whether and how it uses cache. There are other user share settings that you should also pay attention to, especially Minimum Free, which should be set larger than the largest file you expect to write to the share. If a disk has less than Minimum Free, unRAID will choose a different disk when it begins to write a file. If a disk runs out of space when writing a file, the write will fail. There is also a Minimum Free setting for the cache drive in Global Share Settings. That comes into play when a cache-yes or cache-prefer user share needs to overflow onto the array.

 

Here is a more complete explanation of the various cache settings:

 

https://lime-technology.com/forums/topic/46802-faq-for-unraid-v6/?page=2#comment-537383

 

Most pages in the webUI have help. You can turn on Help for the whole webUI, or just click on a specific setting to get help for it.

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