Comment on I want to build a Mini ITX PC for my home server, where do I start?
sxan@midwest.social 1 week agoShit, that’s a lot of storage. K.
I’ve lived on btrfs for years. I love the filesystem. However, RAID had been unreliable for a decade now, with no indication that it will ever be fixed; but most importantly, neither btrfs not zfs have prioritized multi-device support, and bcachefs does.
You can configure a filesystem built from an SSD, a hard drive, and a USB drive, and configure it so that writes and reads go to the SSD first, and are eventually replicated to the hard drive, and eventually eventually to the USB drive. All behind the scenes, so you’re working at SSD speeds for R/W, even if the USB hasn’t yet gotten all of the changes. With btrfs and zfs, you’re working at the speed of the slowest device in your multi-device FS; with bcachefs, you work at the speed of the fastest.
There’s a lot in there I don’t know about yet, like: can it be configured s.t. the fastest is an LRU? But from what I read, it’s designed very similar to L1/L2 cache and main memory.
sugar_in_your_tea@sh.itjust.works 1 week ago
RAID is production ready on btrfs, the only issue is the write hole on RAID 5/6. If you don’t need RAID 5/6, you’re fine. I use RAID 1, which is 100% production ready.
Ah, I’ve never considered that use case. My HDD RAID 1 array is plenty fast for what I need.
But isn’t that basically what a cache drive does? It mostly caches reads, but I think it can cache writes too.
Good to know if that’s your use case, but it sounds pretty niche to me.
sxan@midwest.social 1 week ago
It actually is RAID5/6 I’m looking for. Striping for speed isn’t important to my, and simple redundancy at a cost of 1/2 your total capacity isn’t a nice as getting 3/5 of your total capacity while having drive failure protection and redundancy.
Used to go the device mapper and LVM route, but it was a administrative nightmare for a self-hoster. I only used the commands when something went wrong, which was infrequent enough that I’d forget everything between events and need to re-learn it while worrying that something else would fail while I was fixing it. And changing distros was a nightmare. I use the btrfs command enough for other things to keep it reasonably fresh; if it could reliably do RAID5, I’d have RAID5 again instead of limping along with no RAID and relying on snapshots, backups, and long outages when drives fail.
Multi device is only niche because nothing else supports it yet. I’ll bet once bcachefs becomes more standard (or, if, given the main author of the project), you’ll see it a lot more. The ability to use your M.2 but have eventual consistency replication to one or more slower USB drives without performance impact will be game changing. I’ve been wondering whether this will be usable with network mounted shares as level-3 replication. It’s a fascinating concept.