JorgeB Posted December 31, 2016 Share Posted December 31, 2016 I'm starting to experiment with btrfs on some of my servers, I really like some of its features, especially the data and metadata CRCs. By default btrfs uses the DUP profile for metadata on single devices (except if an SSD is detected since it would basically be a waste of space), and from what I've read this can be very useful at the expense of very little extra space used, e.g., 1TB of data, mostly medium size files, 300MB to 1.5GB: btrfs fi df /mnt/disk9 Data, single: total=997.01GiB, used=987.37GiB System, DUP: total=32.00MiB, used=128.00KiB Metadata, DUP: total=2.00GiB, used=1.09GiB GlobalReserve, single: total=512.00MiB, used=0.00B An extra 2GB allocated for every TB of data for a little extra protection seems like a good deal to me, and for now I'm converting the metadata to DUP after the disk is formatted by unRAID. I believe that unRAID redundancy should make it unnecessary in most cases, but it's not that uncommon to have disk go unmountable when it red balls, so unless there's some reason I'm missing why not use metadata DUP by default on array data disks? Quote Link to comment
limetech Posted January 2, 2017 Share Posted January 2, 2017 why not use metadata DUP by default on array data disks? Probably a good idea. Quote Link to comment
JorgeB Posted August 10, 2018 Author Share Posted August 10, 2018 Wanted to bump this in case it fell through the cracks, as it seems a simple change and IMO an important one, was just today reading a post on the btrfs mailing list where one of the developers writes: Quote raid0 and single profiles are not a good idea for metadata if you want a filesystem that can persist across reboots (some use cases don't require persistence, so they canuse -msingle/-mraid0 btrfs as a large-scale tmpfs). I manually convert all my disks to DUP metadata after formatting, but most users will be unaware of this. 1 Quote Link to comment
-Daedalus Posted August 10, 2018 Share Posted August 10, 2018 Can someone ELI5 this? What makes this DUP profile in particular great? Quote Link to comment
BRiT Posted August 10, 2018 Share Posted August 10, 2018 It adds error recovery for filesystem metadata. Quote Link to comment
JorgeB Posted August 11, 2018 Author Share Posted August 11, 2018 Yes, say a disk gets a bad sector where a metadata chunk is, it will use the other copy to recover, if there's metadata corruption you can lose the whole disk. Quote Link to comment
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