On Mon, Jun 6, 2016 at 10:02 PM, Kai Hendry <[email protected]> wrote: > Sorry I unsubscribed from [email protected] since the traffic > was a bit too high for me. > > On Tue, 7 Jun 2016, at 11:42 AM, Chris Murphy wrote: >> Your command turned this from a 3 drive volume into a 2 drive volume, >> it removed the drive you asked to be removed. > > I actually had 2 drives to begin with, but it wouldn't allow me to > delete the drive without adding a new one, so I had 3 drives.
Two drive raid1 is the minimum number of drives, that's why it won't allow you to delete one. > > I think I've confused you by my talk of "RAID-1 over 3 drives". I am not > sure why RAIDX terminology is so confusing. All I want is for the data > on one drive to be mirrored across them all. So if I add X drives, I > want to X exact copies. But IIUC this changes the RAID level and > everyone gets confused what I am talking about. Yeah you're confused about both RAID in general and how Btrfs raid works. There is no guarantee of X drives meaning X copies with any RAID-1. The mkfs.btrfs man page makes it very clear that there are only ever two copies of data with Btrfs raid1 no matter how many drives you include. > > >> You're definitely missing something but once you understand how it >> actually works, it'll be interesting if you have suggestions on how >> the existing documentation confused you into making this mistake. > > > Summary: I issued the remove command when I should have just removed it > physically IIUC. Yes, but that only works with a two drive Btrfs raid1. The minimum number of drives for successful degraded mount is n-1 drives. You can only lose 1 drive with Btrfs raid1 volumes, you must have all of the other drives for it to be mountable degraded. > If I was to do this again, I would unmount the raid1 mount. Take a disk > physically out and then add the new one. So yes, it would be degraded > but then as you mention, the newly drive will sort it out. One would > hope. Btrfs isn't mature enough to hope for the best. You definitely need to understand it. There's a lot less you need to understand than mdadm or LVM plus other file system stuff, but there's still minimum knowledge required and also there are gotchas that aren't always obvious. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
