How to remove missing device on RAID1?

How to remove missing device on RAID1?

[Kyle Manna]

Hi all,

I have a collection of three (was 4) 1-2TB devices with data and
metadata in a RAID1 mirror.  Last night I was struck by the Click of
Death on an old Samsung drive.

I removed the device from the system, rebooted and mounted the volume
with `-o degraded` and the file system seems fine and usable.  I'm
waiting on a replacement, drive but want to remove the old drive and
re-balance in the meantime.

How do I remove the missing device?  I tried the `btrfs device delete
missing /mnt` but was greeted with "ERROR: missing is not a block
device".  A quick look at that btrfs-progs git repo shows that
`stat("missing")` is called, which of course fails since missing isn't
a block device.  Nothing other then `btrfs replace` seemed intuitive
and all the docs mention the older command.  What's the move?

Thanks!
- Kyle

Versions:
Kernel: 4.2.3-1-ARCH
btrfs-progs: 4.2.2-1
ᐧ

Re: How to remove missing device on RAID1?

[Philip Seeger]

Hi Kyle,

On 10/20/2015 07:24 PM, Kyle Manna wrote:
> I removed the device from the system, rebooted and mounted the volume
> with `-o degraded` and the file system seems fine and usable.  I'm
> waiting on a replacement, drive but want to remove the old drive and
> re-balance in the meantime.

This won't answer your question (not sure why missing doesn't work 
anymore), but you could wait for the replacement and then run "btrfs 
replace start 1 /dev/sdd /mnt", where 1 is the devid of the missing 
drive (dmesg will tell you) and /dev/sdd is the new drive. This way, the 
drive will keep its devid, which may be useful if the ids are used to 
identify the drives (mirror will still have id 1 as first drive and id 2 
as second drive as opposed to 2 = first and 3 = second).



Philip

Re: How to remove missing device on RAID1?

[Goffredo Baroncelli]

On 2015-10-20 19:24, Kyle Manna wrote:
> Hi all,
[...]
> How do I remove the missing device?  I tried the `btrfs device delete
> missing /mnt` but was greeted with "ERROR: missing is not a block
> device".  A quick look at that btrfs-progs git repo shows that
> `stat("missing")` is called, which of course fails since missing isn't
> a block device.  Nothing other then `btrfs replace` seemed intuitive
> and all the docs mention the older command.  What's the move?

In the past the device name was passed directly to the kernel, which operated in an appropriate manner if it was "missing".

The commit e3c9596d3fc8b0df647a6cbae55c2d77570de759 introduced a check so if the argument is not a real device, an error is raised.

So, now, if "missing" is passed, btrfs(-progs) stops because it is not a real device.

This change is quite old (dec 2013); however it seems that this is the first time that a complaint is raised.


> 
> Thanks!
> - Kyle
> 
> Versions:
> Kernel: 4.2.3-1-ARCH
> btrfs-progs: 4.2.2-1
> ᐧ
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 


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Re: How to remove missing device on RAID1?

[Duncan]

Kyle Manna posted on Tue, 20 Oct 2015 10:24:48 -0700 as excerpted:

> Hi all,
> 
> I have a collection of three (was 4) 1-2TB devices with data and
> metadata in a RAID1 mirror.  Last night I was struck by the Click of
> Death on an old Samsung drive.
> 
> I removed the device from the system, rebooted and mounted the volume
> with `-o degraded` and the file system seems fine and usable.  I'm
> waiting on a replacement, drive but want to remove the old drive and
> re-balance in the meantime.
> 
> How do I remove the missing device?  I tried the `btrfs device delete
> missing /mnt` but was greeted with "ERROR: missing is not a block
> device".  A quick look at that btrfs-progs git repo shows that
> `stat("missing")` is called, which of course fails since missing isn't a
> block device.  Nothing other then `btrfs replace` seemed intuitive and
> all the docs mention the older command.  What's the move?
> 
> Thanks!
> - Kyle
> 
> Versions:
> Kernel: 4.2.3-1-ARCH
> btrfs-progs: 4.2.2-1 ᐧ

I believe the current advice given here (that you were likely trying to 
follow, wrapped link)...

https://btrfs.wiki.kernel.org/index.php/
Using_Btrfs_with_Multiple_Devices#Replacing_failed_devices

... is dated and no longer works due to code change some time in the past.

There's a set of (very) recent patches, to the kernel and userspace both 
(I just updated userspace and it's in the git devel-branch v4.2.3-49-
g4db87a1 I just built, kernelspace, I don't see it in linus-mainline yet, 
so I'd guess it's in the btrfs-integration patches, to land in the v4.4 
commit window if not in 4.3 as it's getting late in the cycle for that.

btrfs fi show <path>

That will list the btrfs component devices together with their devids.

Then use the appropriate devid like so:

btrfs dev del <devid> <path>

The -progs commit is d462081f, by Anand Jain, titled:

btrfs-progs: Introduce device delete by devid

According to it, the required kernel commit (title only listed) is 
similar:

Btrfs: Introduce device delete by devid

You can probably find them on-list if you wish to cherry-pick them into a 
current version.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

Re: How to remove missing device on RAID1?

[Kyle Manna]

Thanks for the follow-up Duncan, that makes sense.  I assumed I was
doing something wrong.

I downloaded the devel branch of of btrfs-progs and got it running
before I saw the need for a kernel patch and decided to wait.

For anyone following this later, I needed to use the following to get
the missing device ID:

btrfs device usage <path>
ᐧ

On Tue, Oct 20, 2015 at 1:58 PM, Duncan <1i5t5.duncan@cox.net> wrote:
> Kyle Manna posted on Tue, 20 Oct 2015 10:24:48 -0700 as excerpted:
>
>> Hi all,
>>
>> I have a collection of three (was 4) 1-2TB devices with data and
>> metadata in a RAID1 mirror.  Last night I was struck by the Click of
>> Death on an old Samsung drive.
>>
>> I removed the device from the system, rebooted and mounted the volume
>> with `-o degraded` and the file system seems fine and usable.  I'm
>> waiting on a replacement, drive but want to remove the old drive and
>> re-balance in the meantime.
>>
>> How do I remove the missing device?  I tried the `btrfs device delete
>> missing /mnt` but was greeted with "ERROR: missing is not a block
>> device".  A quick look at that btrfs-progs git repo shows that
>> `stat("missing")` is called, which of course fails since missing isn't a
>> block device.  Nothing other then `btrfs replace` seemed intuitive and
>> all the docs mention the older command.  What's the move?
>>
>> Thanks!
>> - Kyle
>>
>> Versions:
>> Kernel: 4.2.3-1-ARCH
>> btrfs-progs: 4.2.2-1 ᐧ
>
> I believe the current advice given here (that you were likely trying to
> follow, wrapped link)...
>
> https://btrfs.wiki.kernel.org/index.php/
> Using_Btrfs_with_Multiple_Devices#Replacing_failed_devices
>
> ... is dated and no longer works due to code change some time in the past.
>
> There's a set of (very) recent patches, to the kernel and userspace both
> (I just updated userspace and it's in the git devel-branch v4.2.3-49-
> g4db87a1 I just built, kernelspace, I don't see it in linus-mainline yet,
> so I'd guess it's in the btrfs-integration patches, to land in the v4.4
> commit window if not in 4.3 as it's getting late in the cycle for that.
>
> btrfs fi show <path>
>
> That will list the btrfs component devices together with their devids.
>
> Then use the appropriate devid like so:
>
> btrfs dev del <devid> <path>
>
> The -progs commit is d462081f, by Anand Jain, titled:
>
> btrfs-progs: Introduce device delete by devid
>
> According to it, the required kernel commit (title only listed) is
> similar:
>
> Btrfs: Introduce device delete by devid
>
> You can probably find them on-list if you wish to cherry-pick them into a
> current version.
>
> --
> Duncan - List replies preferred.   No HTML msgs.
> "Every nonfree program has a lord, a master --
> and if you use the program, he is your master."  Richard Stallman
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: How to remove missing device on RAID1?

[Henk Slager]

I had a similar issue some time ago, around the time kernel 4.1.6 was
just there.
In case you don't want to wait for new disk or decide to just run the
filesystem with 1 disk less or maybe later on replace 1 of the still
healthy disks with a double/bigger sized one and use current/older
kernel+tools, you could do this (assuming the filesystem is not too
full of course):
- mount degraded
- btrfs balance start -f -v -sdevid=1 -sdevid=1 -sdevid=1 <mountpoint>
  (where missing disk has devid 1)
After completion the (virtual/missing) device shall be fully unallocated
- create /dev/loopX with sparse file of same size as missing disk on
some other filesystem
- btrfs replace start 1 /dev/loopX <mountpoint>
- remove /dev/loopX from the filesystem
- remount filesystyem without degraded
And remove /dev/loopX


On Tue, Oct 20, 2015 at 11:48 PM, Kyle Manna <2bluesc@gmail.com> wrote:
> Thanks for the follow-up Duncan, that makes sense.  I assumed I was
> doing something wrong.
>
> I downloaded the devel branch of of btrfs-progs and got it running
> before I saw the need for a kernel patch and decided to wait.
>
> For anyone following this later, I needed to use the following to get
> the missing device ID:
>
> btrfs device usage <path>
> ᐧ
>
> On Tue, Oct 20, 2015 at 1:58 PM, Duncan <1i5t5.duncan@cox.net> wrote:
>> Kyle Manna posted on Tue, 20 Oct 2015 10:24:48 -0700 as excerpted:
>>
>>> Hi all,
>>>
>>> I have a collection of three (was 4) 1-2TB devices with data and
>>> metadata in a RAID1 mirror.  Last night I was struck by the Click of
>>> Death on an old Samsung drive.
>>>
>>> I removed the device from the system, rebooted and mounted the volume
>>> with `-o degraded` and the file system seems fine and usable.  I'm
>>> waiting on a replacement, drive but want to remove the old drive and
>>> re-balance in the meantime.
>>>
>>> How do I remove the missing device?  I tried the `btrfs device delete
>>> missing /mnt` but was greeted with "ERROR: missing is not a block
>>> device".  A quick look at that btrfs-progs git repo shows that
>>> `stat("missing")` is called, which of course fails since missing isn't a
>>> block device.  Nothing other then `btrfs replace` seemed intuitive and
>>> all the docs mention the older command.  What's the move?
>>>
>>> Thanks!
>>> - Kyle
>>>
>>> Versions:
>>> Kernel: 4.2.3-1-ARCH
>>> btrfs-progs: 4.2.2-1 ᐧ
>>
>> I believe the current advice given here (that you were likely trying to
>> follow, wrapped link)...
>>
>> https://btrfs.wiki.kernel.org/index.php/
>> Using_Btrfs_with_Multiple_Devices#Replacing_failed_devices
>>
>> ... is dated and no longer works due to code change some time in the past.
>>
>> There's a set of (very) recent patches, to the kernel and userspace both
>> (I just updated userspace and it's in the git devel-branch v4.2.3-49-
>> g4db87a1 I just built, kernelspace, I don't see it in linus-mainline yet,
>> so I'd guess it's in the btrfs-integration patches, to land in the v4.4
>> commit window if not in 4.3 as it's getting late in the cycle for that.
>>
>> btrfs fi show <path>
>>
>> That will list the btrfs component devices together with their devids.
>>
>> Then use the appropriate devid like so:
>>
>> btrfs dev del <devid> <path>
>>
>> The -progs commit is d462081f, by Anand Jain, titled:
>>
>> btrfs-progs: Introduce device delete by devid
>>
>> According to it, the required kernel commit (title only listed) is
>> similar:
>>
>> Btrfs: Introduce device delete by devid
>>
>> You can probably find them on-list if you wish to cherry-pick them into a
>> current version.
>>
>> --
>> Duncan - List replies preferred.   No HTML msgs.
>> "Every nonfree program has a lord, a master --
>> and if you use the program, he is your master."  Richard Stallman
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: How to remove missing device on RAID1?

[Henk Slager]

copy-paste error corrected
On Wed, Oct 21, 2015 at 12:40 AM, Henk Slager <hslager@hotmail.com> wrote:
> I had a similar issue some time ago, around the time kernel 4.1.6 was
> just there.
> In case you don't want to wait for new disk or decide to just run the
> filesystem with 1 disk less or maybe later on replace 1 of the still
> healthy disks with a double/bigger sized one and use current/older
> kernel+tools, you could do this (assuming the filesystem is not too
> full of course):
> - mount degraded
- btrfs balance start -f -v -sdevid=1 -mdevid=1 -mdevid=1 <mountpoint>
>   (where missing disk has devid 1)
> After completion the (virtual/missing) device shall be fully unallocated
> - create /dev/loopX with sparse file of same size as missing disk on
> some other filesystem
> - btrfs replace start 1 /dev/loopX <mountpoint>
> - remove /dev/loopX from the filesystem
> - remount filesystyem without degraded
> And remove /dev/loopX
>
>
> On Tue, Oct 20, 2015 at 11:48 PM, Kyle Manna <2bluesc@gmail.com> wrote:
>> Thanks for the follow-up Duncan, that makes sense.  I assumed I was
>> doing something wrong.
>>
>> I downloaded the devel branch of of btrfs-progs and got it running
>> before I saw the need for a kernel patch and decided to wait.
>>
>> For anyone following this later, I needed to use the following to get
>> the missing device ID:
>>
>> btrfs device usage <path>
>> ᐧ
>>
>> On Tue, Oct 20, 2015 at 1:58 PM, Duncan <1i5t5.duncan@cox.net> wrote:
>>> Kyle Manna posted on Tue, 20 Oct 2015 10:24:48 -0700 as excerpted:
>>>
>>>> Hi all,
>>>>
>>>> I have a collection of three (was 4) 1-2TB devices with data and
>>>> metadata in a RAID1 mirror.  Last night I was struck by the Click of
>>>> Death on an old Samsung drive.
>>>>
>>>> I removed the device from the system, rebooted and mounted the volume
>>>> with `-o degraded` and the file system seems fine and usable.  I'm
>>>> waiting on a replacement, drive but want to remove the old drive and
>>>> re-balance in the meantime.
>>>>
>>>> How do I remove the missing device?  I tried the `btrfs device delete
>>>> missing /mnt` but was greeted with "ERROR: missing is not a block
>>>> device".  A quick look at that btrfs-progs git repo shows that
>>>> `stat("missing")` is called, which of course fails since missing isn't a
>>>> block device.  Nothing other then `btrfs replace` seemed intuitive and
>>>> all the docs mention the older command.  What's the move?
>>>>
>>>> Thanks!
>>>> - Kyle
>>>>
>>>> Versions:
>>>> Kernel: 4.2.3-1-ARCH
>>>> btrfs-progs: 4.2.2-1 ᐧ
>>>
>>> I believe the current advice given here (that you were likely trying to
>>> follow, wrapped link)...
>>>
>>> https://btrfs.wiki.kernel.org/index.php/
>>> Using_Btrfs_with_Multiple_Devices#Replacing_failed_devices
>>>
>>> ... is dated and no longer works due to code change some time in the past.
>>>
>>> There's a set of (very) recent patches, to the kernel and userspace both
>>> (I just updated userspace and it's in the git devel-branch v4.2.3-49-
>>> g4db87a1 I just built, kernelspace, I don't see it in linus-mainline yet,
>>> so I'd guess it's in the btrfs-integration patches, to land in the v4.4
>>> commit window if not in 4.3 as it's getting late in the cycle for that.
>>>
>>> btrfs fi show <path>
>>>
>>> That will list the btrfs component devices together with their devids.
>>>
>>> Then use the appropriate devid like so:
>>>
>>> btrfs dev del <devid> <path>
>>>
>>> The -progs commit is d462081f, by Anand Jain, titled:
>>>
>>> btrfs-progs: Introduce device delete by devid
>>>
>>> According to it, the required kernel commit (title only listed) is
>>> similar:
>>>
>>> Btrfs: Introduce device delete by devid
>>>
>>> You can probably find them on-list if you wish to cherry-pick them into a
>>> current version.
>>>
>>> --
>>> Duncan - List replies preferred.   No HTML msgs.
>>> "Every nonfree program has a lord, a master --
>>> and if you use the program, he is your master."  Richard Stallman
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: How to remove missing device on RAID1?

[Kyle Manna]

Hi Henk,

This trick/hack worked great for me.  After the rebalance was
complete, a sparse file + loop device, `btrfs replace` and `btrfs
delete` worked as expected.  Thanks.

In other news, I did hit a btrfs bug 3 times while attempting to
balance.  I've added my comments @
https://bugzilla.kernel.org/show_bug.cgi?id=105681#c14
ᐧ

On Tue, Oct 20, 2015 at 3:46 PM, Henk Slager <hslager@hotmail.com> wrote:
> copy-paste error corrected
> On Wed, Oct 21, 2015 at 12:40 AM, Henk Slager <hslager@hotmail.com> wrote:
>> I had a similar issue some time ago, around the time kernel 4.1.6 was
>> just there.
>> In case you don't want to wait for new disk or decide to just run the
>> filesystem with 1 disk less or maybe later on replace 1 of the still
>> healthy disks with a double/bigger sized one and use current/older
>> kernel+tools, you could do this (assuming the filesystem is not too
>> full of course):
>> - mount degraded
> - btrfs balance start -f -v -sdevid=1 -mdevid=1 -mdevid=1 <mountpoint>
>>   (where missing disk has devid 1)
>> After completion the (virtual/missing) device shall be fully unallocated
>> - create /dev/loopX with sparse file of same size as missing disk on
>> some other filesystem
>> - btrfs replace start 1 /dev/loopX <mountpoint>
>> - remove /dev/loopX from the filesystem
>> - remount filesystyem without degraded
>> And remove /dev/loopX
>>
>>
>> On Tue, Oct 20, 2015 at 11:48 PM, Kyle Manna <2bluesc@gmail.com> wrote:
>>> Thanks for the follow-up Duncan, that makes sense.  I assumed I was
>>> doing something wrong.
>>>
>>> I downloaded the devel branch of of btrfs-progs and got it running
>>> before I saw the need for a kernel patch and decided to wait.
>>>
>>> For anyone following this later, I needed to use the following to get
>>> the missing device ID:
>>>
>>> btrfs device usage <path>
>>> ᐧ
>>>
>>> On Tue, Oct 20, 2015 at 1:58 PM, Duncan <1i5t5.duncan@cox.net> wrote:
>>>> Kyle Manna posted on Tue, 20 Oct 2015 10:24:48 -0700 as excerpted:
>>>>
>>>>> Hi all,
>>>>>
>>>>> I have a collection of three (was 4) 1-2TB devices with data and
>>>>> metadata in a RAID1 mirror.  Last night I was struck by the Click of
>>>>> Death on an old Samsung drive.
>>>>>
>>>>> I removed the device from the system, rebooted and mounted the volume
>>>>> with `-o degraded` and the file system seems fine and usable.  I'm
>>>>> waiting on a replacement, drive but want to remove the old drive and
>>>>> re-balance in the meantime.
>>>>>
>>>>> How do I remove the missing device?  I tried the `btrfs device delete
>>>>> missing /mnt` but was greeted with "ERROR: missing is not a block
>>>>> device".  A quick look at that btrfs-progs git repo shows that
>>>>> `stat("missing")` is called, which of course fails since missing isn't a
>>>>> block device.  Nothing other then `btrfs replace` seemed intuitive and
>>>>> all the docs mention the older command.  What's the move?
>>>>>
>>>>> Thanks!
>>>>> - Kyle
>>>>>
>>>>> Versions:
>>>>> Kernel: 4.2.3-1-ARCH
>>>>> btrfs-progs: 4.2.2-1 ᐧ
>>>>
>>>> I believe the current advice given here (that you were likely trying to
>>>> follow, wrapped link)...
>>>>
>>>> https://btrfs.wiki.kernel.org/index.php/
>>>> Using_Btrfs_with_Multiple_Devices#Replacing_failed_devices
>>>>
>>>> ... is dated and no longer works due to code change some time in the past.
>>>>
>>>> There's a set of (very) recent patches, to the kernel and userspace both
>>>> (I just updated userspace and it's in the git devel-branch v4.2.3-49-
>>>> g4db87a1 I just built, kernelspace, I don't see it in linus-mainline yet,
>>>> so I'd guess it's in the btrfs-integration patches, to land in the v4.4
>>>> commit window if not in 4.3 as it's getting late in the cycle for that.
>>>>
>>>> btrfs fi show <path>
>>>>
>>>> That will list the btrfs component devices together with their devids.
>>>>
>>>> Then use the appropriate devid like so:
>>>>
>>>> btrfs dev del <devid> <path>
>>>>
>>>> The -progs commit is d462081f, by Anand Jain, titled:
>>>>
>>>> btrfs-progs: Introduce device delete by devid
>>>>
>>>> According to it, the required kernel commit (title only listed) is
>>>> similar:
>>>>
>>>> Btrfs: Introduce device delete by devid
>>>>
>>>> You can probably find them on-list if you wish to cherry-pick them into a
>>>> current version.
>>>>
>>>> --
>>>> Duncan - List replies preferred.   No HTML msgs.
>>>> "Every nonfree program has a lord, a master --
>>>> and if you use the program, he is your master."  Richard Stallman
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: How to remove missing device on RAID1?

[Dmitry Katsubo]

On 2015-10-21 00:40, Henk Slager wrote:
> I had a similar issue some time ago, around the time kernel 4.1.6 was
> just there.
> In case you don't want to wait for new disk or decide to just run the
> filesystem with 1 disk less or maybe later on replace 1 of the still
> healthy disks with a double/bigger sized one and use current/older
> kernel+tools, you could do this (assuming the filesystem is not too
> full of course):
> - mount degraded
> - btrfs balance start -f -v -sdevid=1 -sdevid=1 -sdevid=1 <mountpoint>
>   (where missing disk has devid 1)

Am I right that one can "btrfs dev delete 1" after balance succeeded?

> After completion the (virtual/missing) device shall be fully unallocated
> - create /dev/loopX with sparse file of same size as missing disk on
> some other filesystem
> - btrfs replace start 1 /dev/loopX <mountpoint>
> - remove /dev/loopX from the filesystem
> - remount filesystyem without degraded
> And remove /dev/loopX

If would be nice if btrfs allows to delete device and perform rebalance
automatically (provided that left devices still have enough space to
sustain raidX prerequisite).

-- 
With best regards,
Dmitry

Re: How to remove missing device on RAID1?

[Henk Slager]

On Wed, Oct 21, 2015 at 11:54 AM, Dmitry Katsubo
<dmitry.katsubo@gmail.com> wrote:
> On 2015-10-21 00:40, Henk Slager wrote:
>> I had a similar issue some time ago, around the time kernel 4.1.6 was
>> just there.
>> In case you don't want to wait for new disk or decide to just run the
>> filesystem with 1 disk less or maybe later on replace 1 of the still
>> healthy disks with a double/bigger sized one and use current/older
>> kernel+tools, you could do this (assuming the filesystem is not too
>> full of course):
>> - mount degraded
>> - btrfs balance start -f -v -sdevid=1 -mdevid=1 -ddevid=1 <mountpoint>
>>   (where missing disk has devid 1)
>
> Am I right that one can "btrfs dev delete 1" after balance succeeded?
If the patch that Ducan decribes is applied, then yes, this is then
the way to remove (delete) the missing device from the filesystem.

>> After completion the (virtual/missing) device shall be fully unallocated
>> - create /dev/loopX with sparse file of same size as missing disk on
>> some other filesystem
>> - btrfs replace start 1 /dev/loopX <mountpoint>
>> - remove /dev/loopX from the filesystem
>> - remount filesystyem without degraded
>> And remove /dev/loopX
>
> If would be nice if btrfs allows to delete device and perform rebalance
> automatically (provided that left devices still have enough space to
> sustain raidX prerequisite).
This would indeed be nice, but I guess it should be working already,
looking at older (3.x) btrfs-tools documentation. It's just that it
could not be used for some time. Anyhow, once this patch is more
commonly available, people can test/use it and see if still a manual
extra specific balance is needed in order to get rid of or work-around
issues. It is actually the functionality of the '-r' option of 'btrfs
replace' that is then applied.