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Comment by nothrabannosir | Hacker News Reader

It looks like he's trying to say: in an array of N >= 2 drives, "BTRFS RAID 1" will still only choose 2 disks to replicate a file to. It's just 2 different ones for every file.

Well, not every file, but you see the point.

If that's the case, this has the advantage of having a subset of files recoverable even after >1 disk failure. Unlike RAID 5.

On the flip side: read speed is limited to at most 2 concurrent disks. Unlike RAID 5, where it's N-1. But that's theoretical, what's the reality on read speeds in RAID 5?

Anyway, if that's true, that would be a really weird name. Why didn't they call that "BTRFS RAID 5"? A look at the docs doesn't make this clear to me at all. I'm not sure what to believe...

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I was not even aware of this possibility, thanks for explaining it to me.

The concept fills with me with absolute horror though. Losing a part of my files is as bad as losing everything.

The performance benefit with larger files of RAID1 vs RAID5/6 can be very 'substantial'. Even my old 18 TB NAS could achieve 1+ GB/s on sequential reads.

RAID isn't backup. Losing some of your files instead of all your files means you have access to some of the files during the restore window. And your restore might be quicker?

But how do you even fire up an Oracle database with some of the dbf files missing? And I can't think of any other application (other than maybe a document storage system) that would be useful with some of the files missing.

You don't. You rsync the missing files over and skip the data that is already present, saving time.

RAID5/6+ is only as fast as your slowest disk, and seek times are no better. In most respects, mirroring gets you better performance, and for most drive configurations, is more reliable than RAID5. Massive throughput on single files one at a time is not interesting to most people with big storage requirements.

I currently run RAID6 (raidz2) across 10 drives. But I'll be moving to RAID10 before long. Whether using zfs or not, depends on btrfs stability.

RAID5/6 is only as fast as the slowes disk regarding ZFS yes if you talk about random IOPS. BTRFS performance I haven't measured yet.

RAID5/6 random IOPS can be quite good or as you can expect if you use MDADM.

The best solution seems to be tons of RAM for caching and ZFS with SSD SLOG if you need reliable and fast sync writes. But with ZFS, performance comes second over reliability.

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