Re: unable to mount multi disk volume with recovery mode

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

Anand Jain posted on Mon, 14 Sep 2015 17:44:25 +0800 as excerpted:

> Hi Qu,
> 
>> Unfortunately, single mode means no duplication.
>> And degrade mount only works for RAID level with
>> duplication(DUP,RAID1/5/6/10).
> 
> further to the below commit.
> 
>   commit 95669976bd7d30ae265db938ecb46a6b7f8cb893
>      Btrfs: don't consider the missing device when allocating new chunks
> 
> in case of 2-disk RAID1 mounted with only one good disk, we would create
> Single profile and actually the created single profiles are still
> workable with one disk failed. And so the proposed patch below will let
> single profile to be mount in this context..
>    [PATCH 23/23] Btrfs: allow -o rw,degraded for single group profile
> 
> to recover when missing disk is replaced balance convert can migrate
> single profiles back to RAID1 profile.
> 
> Also your explanation for degraded is correct, I am ok to use a new new
> mount option (like auto-reduced-profile ?) if needed / confusing.
> 
> Any comments / feedbacks are welcome.

I'm familiar with the issue, and for all I know it works exactly as 
described, but if so, shouldn't it be changed so that while 2-device 
raid1 mounted with only a single device create single-profile chunks only 
for data, metadata chunk-creation will default back to dup-profile?

If there's a good reason it doesn't, could someone explain it?  It seems 
to me that raid1 already indicates that two copies is wanted, so if it's 
operating degraded with only a single device, shouldn't it go dup, 
particularly for metadata?  (If possible, I'd say for data as well, but 
that's not possible except in mixed-bg-mode.)

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