March 24, 201610 yr Hey, a little new to NAS, looking for help with a usage question. I have a Unraid NAS set up with a 2TB and 8TB drive for storage and a 240GB SSD and 300GB HDD setup as cache drives. I thought the way it would work is the system would leverage the better speeds of the cache drives to write data to quickly during transfers and later move that data to the storage drives. Currently however my cache is sitting as mostly full. Can anyone explain how this works to me please. Also, with my user shares; what difference does it make to have use Cache Disk "on, off, only"?
March 24, 201610 yr Community Expert Hey, a little new to NAS, looking for help with a usage question. I have a Unraid NAS set up with a 2TB and 8TB drive for storage and a 240GB SSD and 300GB HDD setup as cache drives. I thought the way it would work is the system would leverage the better speeds of the cache drives to write data to quickly during transfers and later move that data to the storage drives. Currently however my cache is sitting as mostly full. Can anyone explain how this works to me please. Without knowing what settings you have regarding cache at both the global share level and for each of your individual shares it is difficult to give advice. It is always a good idea when requesting help to provide the diagnostics file (Tools->Diagnostics) as this allows us to see both your logs and how your system is configured. Also, with my user shares; what difference does it make to have use Cache Disk "on, off, only"? Turn on the unRAID Help and it gives a good description of what the different settings do.
March 24, 201610 yr Author I have attached my config files. Thank you for the tip on including this. I don't know how to control global cache options but I have for now have turned use cache disk off for each user share. Previously I had it on for each share. I will switch on help and check that out. Also, is anyone able to advise why my cache drive totals 280GB only when the drives combined should total 540GB? nas-diagnostics-20160325-0019.zip
March 24, 201610 yr Also, is anyone able to advise why my cache drive totals 280GB only when the drives combined should total 540GB? What makes you think they should add together? The default setting for the cache pool in unraid is RAID1, which gives full redundancy in case one of the cache pool members dies.
March 24, 201610 yr Author I guess the answer to what makes me think they should add together is just ignorance. I didn't know so I asked. Thank you for filling me in, that's really cool by the way.
March 24, 201610 yr Community Expert Also, is anyone able to advise why my cache drive totals 280GB only when the drives combined should total 540GB? What makes you think they should add together? The default setting for the cache pool in unraid is RAID1, which gives full redundancy in case one of the cache pool members dies. Actually, even the reported 280GB is too much. Should be 240GB, the size of the smaller drive. The real calculation gets a little more complicated if you have more than 2 drives in the pool. btrfs disk usage calculator
March 24, 201610 yr Author Weird. That could have something to do with why the used portion of the cache is 238GB.
March 24, 201610 yr Community Expert And since one of the drives isn't SSD you probably won't get SSD performance. HDD cache is plenty fast for caching writes over the network though.
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