mbc0 Posted February 11, 2019 Share Posted February 11, 2019 Hi, I set up a cache pool of 3 x 500GB SSD's but it is being reported as 1.5TB? surely this should be 1TB with 500GB Parity? Quote Link to comment
John_M Posted February 11, 2019 Share Posted February 11, 2019 According to the btrfs calculator (set the number of devices to 3 and choose the RAID-5 profile) you should have 960 GB of space available from three 480 GB disks so, no, it isn't correct. I'd like to be able to use RAID-5 myself but it is currently not advised because it is buggy and there's a serious risk of data loss. You ought to switch to RAID-1 instead. That will give you 720 GB of space and your data will be much safer. 1 Quote Link to comment
mbc0 Posted February 11, 2019 Author Share Posted February 11, 2019 ok, will change to raid 1, is there any threads I can watch or find out when raid5 is useable? Thanks for the info! 🙂 Quote Link to comment
John_M Posted February 11, 2019 Share Posted February 11, 2019 The btrfs wiki. The major problem with RAID-5 and 6 is the "write hole". Quote Link to comment
mbc0 Posted February 11, 2019 Author Share Posted February 11, 2019 ok, so btrfs problem, not an unRAID problem... Thank you, converting to RAID1 now Quote Link to comment
JorgeB Posted February 11, 2019 Share Posted February 11, 2019 Currently btrfs raid5/raid6 report the free space without accounting for parity, used space is correctly reported, it's still not implemented in the btrfs tools. Quote Link to comment
mbc0 Posted February 11, 2019 Author Share Posted February 11, 2019 Just now, johnnie.black said: Currently btrfs raid5/raid6 report the free space without accounting for parity, used space is correctly reported, it's still not implemented in the btrfs tools. That's a real shame, I bought an extra 2 500GB SSD's for performance & redundancy but just ended up with redundancy 😞 I see post's going back years for Raid5 issues with btrfs so I guess this isn't something going to be fixed imminently! Quote Link to comment
JorgeB Posted February 11, 2019 Share Posted February 11, 2019 Most issues with btrfs raid5 are fixed on current kernel, I have several raid5/6 pools myself running perfectly for a few months, remaining issue is basically the write hole problem if there's an unclean shutdown, that issue affects most raid5/6 implementations, not just btrfs, UPS is recommended to minimize the risk. Quote Link to comment
John_M Posted February 11, 2019 Share Posted February 11, 2019 I'm not that brave but I find RAID-10 useful. Something to consider if you feel you can justify buying a fourth SSD. Quote Link to comment
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