July 18, 20169 yr Just added a 2nd cache drive for the first time and it doesn't look to be loading some of the information. Is this expected? Thanks!
July 18, 20169 yr Author Am I misunderstanding how multiple cache drives work? Does it not add on the additional space? If so why does it not show the space you have? Thanks!
July 18, 20169 yr Cache drives are organised into a cache pool using btrfs. Think of it kinda like RAID 5, If you have 2 drives they will act like a RAID 1 mirrored array. So if you have 1 250GB drive you will have 250GB total. If you add a second 250GB drive you will still have 250GB total but it will now be protected with a mirror. In your case if you now added a 3rd 250GB SSD to the cache pool your total should go up to around 500GB.
July 18, 20169 yr Author Cache drives are organised into a cache pool using btrfs. Think of it kinda like RAID 5, If you have 2 drives they will act like a RAID 1 mirrored array. So if you have 1 250GB drive you will have 250GB total. If you add a second 250GB drive you will still have 250GB total but it will now be protected with a mirror. In your case if you now added a 3rd 250GB SSD to the cache pool your total should go up to around 500GB. Thank you for the clarification
July 18, 20169 yr Just to round it off, it is also possible to change the cache pool behavior. I for one use 2 ssd cache drives in a stripe/raid0-ish setup. Each drive has 256 GB while I total at ~500 GB storage with "about the throughput" of 2 drives. You can change the setting by left clicking the blue "Cache" in your array and then scroll down to balancing. Might want to turn on the help to know what you are doing. I do not recommend making any changes there unless you know what you are doing though. I have the feeling that there is some dupe-data control as I got more space then I should have - with vms I certainly would have a lot of duplicate data. I like this setup, as it allows me to take both, speed and size advantages over putting each vms on it's own disk(outside of the array for instance), but it is more likely to loose data on all vms if a single ssd dies - it is a cache after all. Surprisingly for me - it is quite easy to switch between the modes, or simply change after installing a second or "n" drive. Takes a while though.
July 18, 20169 yr Community Expert Cache drives are organised into a cache pool using btrfs. Think of it kinda like RAID 5, If you have 2 drives they will act like a RAID 1 mirrored array. So if you have 1 250GB drive you will have 250GB total. If you add a second 250GB drive you will still have 250GB total but it will now be protected with a mirror. In your case if you now added a 3rd 250GB SSD to the cache pool your total should go up to around 500GB. Correct answer for this scenario is 375. btrfs disk usage calculator
April 23, 20179 yr Community Expert 1 hour ago, Joe said: trurl - NeoDude is correct. 500GB in Raid 5 with 3 - 250GB Drives. Joe If he had said btrfs raid5 instead of "kinda like RAID 5" I would have agreed. But nobody on the thread actually said that. The default is btrfs raid1 and unless you specify btrfs raid5 you won't get it. And according to our FAQ, raid5/6 isn't recommended
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