Re: what is the best way to monitor raid1 drive failures?

[Duncan <1i5t5.duncan@cox.net>]

Suman C posted on Tue, 14 Oct 2014 07:48:01 -0700 as excerpted:

> Here's a simple raid1 recovery experiment that's not working as
> expected.
> 
> kernel: 3.17, latest mainline progs: 3.16.1
> 
> I started with a simple raid1 mirror of 2 drives (sda and sdb). The
> filesystem is functional, I created one subvol, put some data,
> read/write tested etc..
> 
> yanked the sdb out. (this is physical/hardware). btrfs fi show prints
> drive missing, as expected.
> 
> powered the machine down. removed the "bad"(yanked out sdb) drive and
> replaced it with a new drive. Powered up the machine.
> 
> The new drive shows up as sdb. btrfs fi show still prints drive missing.
> 
> mounted the filesystem with ro,degraded
> 
> tried adding the "new" sdb drive which results in the following error.
> (-f because the new drive has a fs from past)
> 
> # btrfs device add -f /dev/sdb /mnt2/raid1pool /dev/sdb is mounted

While I'm not sure it'll get you past the error, did you try...

# btrfs replace ...

That's the new way to /replace/ a missing device, adding a new one and 
deleting the old one (which can be missing) at the same time.  See the 
btrfs-replace manpage.

While the btrfs-replace manpage says that you have to use the <devid> 
format if the device is missing, it isn't particularly helpful in telling 
what that format actually is.  Do a btrfs fi show and use the appropriate 
devid /number/ from there. =:^)

Please report back as I'm using btrfs raid1 as well, but my own tests are 
rather stale by this point and I'd have to figure it out as I went.  So 
I'm highly interested in your results. =:^)

(FWIW, personally I'd have made that btrfs device replace, instead of 
btrfs replace, to keep it grouped with the other device operations, but 
whatever, it's its own top-level command, now.  Tho at least the
btrfs-device manpage mentions btrfs replace and its manpage as well.  But 
I still think having replace as its own top-level command is confusing.)

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
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