August 11, 20169 yr I finally got a second cache drive as I wanted my docker image and vm's to be safe if a cache drive fails. I had a 120GB ssd originally and now i added a 250gb ssd. So I was under the impression that these drives are in an effective raid 1? Well its saying that I have 185GB of available space in my cache, which obviously comes from (120+250)/2. Well my question is, the 65GB of extra space wouldn't be mirrored on both drives right? Shouldn't the cache size still be limited to 120GB?
August 11, 20169 yr Community Expert I finally got a second cache drive as I wanted my docker image and vm's to be safe if a cache drive fails. I had a 120GB ssd originally and now i added a 250gb ssd. So I was under the impression that these drives are in an effective raid 1? Well its saying that I have 185GB of available space in my cache, which obviously comes from (120+250)/2. Well my question is, the 65GB of extra space wouldn't be mirrored on both drives right? Shouldn't the cache size still be limited to 120GB? The displayed size is incorrect when drives are not the same size. You are correct that it is limited to the smaller of the two when only 2 drives are used. The calculation gets a little more complicated when more than 2 drives are used. btrfs disk usage calculator
August 11, 20169 yr Author So it will only let me fill up the cache to 120GB even though it says 185GB?
August 11, 20169 yr Community Expert Yes, and I think there have been some people that have corrupted their btrfs by filling it up so don't push it.
August 11, 20169 yr Author I'll try not to fill it up. I usually only use about 15GB max in a day. So this is interesting. I unplugged my 120gb and restarted the array and it showed i 185GB usable again. I shut everything down and plugged the 120gb back in and now its saying 250gb usable. strange.... I had another question about the cache but i forgot what i was going to ask....
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