I did some searching and didn't see anyone with this "issue". It seems as though my unraid box doesn't realize it has a cache drive. This morning I woke up & started transferring ~30GB of data. After wondering at the ~22MB/s transfer speed, I checked the status of my drives only to notice only the parity & target drives were spun up. The cache drive is still sleeping. Why would this be?

 

I'm still running 4.5.4 and the cache drive is currently a 120GB WD. It was an experiment to see if I wanted to stick a performance drive in there (I have a Raptor 150GB that I can move that way once I upgrade to SSD in my desktop) however if it's not even going to be utilized...

I did some searching and didn't see anyone with this "issue". It seems as though my unraid box doesn't realize it has a cache drive. This morning I woke up & started transferring ~30GB of data. After wondering at the ~22MB/s transfer speed, I checked the status of my drives only to notice only the parity & target drives were spun up. The cache drive is still sleeping. Why would this be?

 

I'm still running 4.5.4 and the cache drive is currently a 120GB WD. It was an experiment to see if I wanted to stick a performance drive in there (I have a Raptor 150GB that I can move that way once I upgrade to SSD in my desktop) however if it's not even going to be utilized...

Did you enable it on the user-share you are copying to?

Did you set a minimum free size for it to be used?  If so, exactly what value did you put in the configuration field?

 

Is the cache drive full?  If it has no more free space (less than the configured minimum space), it will not be used.

 

Joe L.

You hit the nail on the head (as usual) Joe.

 

Strangely, every other share had the cache drive enabled except the one I was transferring to. Also, I adjusted the min free size.

 

Do you have any suggestions on how best to set that value? I understand that it will not use the drive if there's not enough free space - is this a check it performs before each copy? If so, I should never run into a situation where I start a large copy, it hits that min free marker then ... who knows what would happen. Or does it keep trying to fill up until the min free space amount then automagically switch directly to the share?

 

Understanding how it would work in this situation might help set that value.

 

Thanks Joe.

You hit the nail on the head (as usual) Joe.

 

Strangely, every other share had the cache drive enabled except the one I was transferring to. Also, I adjusted the min free size.

 

Do you have any suggestions on how best to set that value? I understand that it will not use the drive if there's not enough free space - is this a check it performs before each copy? If so, I should never run into a situation where I start a large copy, it hits that min free marker then ... who knows what would happen. Or does it keep trying to fill up until the min free space amount then automagically switch directly to the share?

 

Understanding how it would work in this situation might help set that value.

 

Thanks Joe.

It is a check before the cache drive is used for any given file.  Most programs transferring files start with an initial empty file and incrimentally fill it as the file is transferred.  It is impossible for unRAID to know the eventual full size.  For that reason, if you routinely transfer 6 Gig files you'll want to set the min-free to a value above that (10 Gig perhaps?).    Once it starts using the drive it can still run out if a single file is larger than the space it needs.

 

Also note: the configuration field is in 1k blocks, so for 10 Gig the value in the config field should be

10000000

Ok that makes sense.

 

So one final question. If I'm transferring say 4x 6GB files and min size is set to 10GB, after say the 3rd file it sees it doesn't have enough room left for the 4th, on my windows box does it throw an error saying it doesn't have enough room to copy or does it then skip the cache drive and finish copying the last file to the target share?

 

I had it set to 5GB (mind you in k) but I think I'll be upping that as suggested. 

 

Oh, and even with this aged 120GB test cache drive, I'm now seeing 47-55MB/s *impressed*! 

Ok that makes sense.

 

So one final question. If I'm transferring say 4x 6GB files and min size is set to 10GB, after say the 3rd file it sees it doesn't have enough room left for the 4th, on my windows box does it throw an error saying it doesn't have enough room to copy or does it then skip the cache drive and finish copying the last file to the target share?

It will skip the cache drive and copy the 4th file directly to the protected array IF that copy is started after the first three are completed.  But, if you start 4 transfers at the exact same time, then at that time there is enough space for any one, but not for all.  When they fill the cache disk one or more will fail when they have no more free space.  Basically any given file must be able to fit in its entirety.

Cool, got it. I *usually* only start a single transfer of multiple files if I have multiples to move so sounds like it works perfectly for me! Thanks for all the info Joe. Now I'm going to have to read up on the (directory) caching stuff I just noticed people talking about