On 2016-06-07 00:02, Kai Hendry wrote:
Sorry I unsubscribed from linux-btrfs@xxxxxxxxxxxxxxx since the traffic
was a bit too high for me.
Entirely understandable, although for what it's worth it's nowhere near
as busy as some other mailing lists (linux-kernel@xxxxxxxxxxxxxxx for
example sees well over a thousand messages a day on average).
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.
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.
Actually, because of how raid1 mode in BTRFS works, you just get 2
copies no matter how many drives you have. Once you add more than the
first two drives, it starts to work more like RAID-10, although slightly
less efficiently than the raid10 profile. This is why you couldn't pull
a single drive out of a 3 drive raid1 set and have all the data.
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. The device delete command is for shrinking arrays, removing
failing disks, or for re-purposing individual drives.
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.
Yes, although you would then need to be certain to run a balance with
-dconvert=raid1 -mconvert=raid1 to clean up anything that got allocated
before the new disk was added.
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