Re: How to replace a failed drive in btrfs RAID 1 filesystem
Andrei Borzenkov posted on Sat, 10 Mar 2018 13:27:03 +0300 as excerpted: > And "missing" is not the answer because I obviously may have more than > one missing device. "missing" is indeed the answer when using btrfs device remove. See the btrfs-device manpage, which explains that if there's more than one device missing, either just the first one described by the metadata will be removed (if missing is only specified once), or missing can be specified multiple times. raid6 with two devices missing is the only normal candidate for that presently, tho on-list we've seen aborted-add cases where it still worked as well, because while the metadata listed the new device it didn't actually have any data when it became apparent it was bad and thus needed to be removed again. Note that because btrfs raid1 and raid10 only does two-way-mirroring regardless of the number of devices, and because of the per-chunk (as opposed to per-device) nature of btrfs raid10, those modes can only expect successful recovery with a single missing device, altho as mentioned above we've seen on-list at least one case where an aborted device-add of device found to be bad after the add didn't actually have anything on it, so it could still be removed along with the device it was originally intended to replace. Of course the N-way-mirroring mode, whenever it eventually gets implemented, will allow missing devices upto N-1, and N-way-parity mode, if it's ever implemented, similar, but N-way-mirroring was scheduled for after raid56 mode so it could make use of some of the same code, and that has of course taken years on years to get merged and stabilize, and there's no sign yet of N-way-mirroring patches, which based on the raid56 case could take years to stabilize and debug after original merge, so the still somewhat iffy raid6 mode is likely to remain the only normal usage of multiple missing for years, yet. For btrfs replace, the manpage says ID's the only way to handle missing, but getting that ID, as you've indicated, could be difficult. For filesystems with only a few devices that haven't had any or many device config changes, it should be pretty easy to guess (a two device filesystem with no changes should have IDs 1 and 2, so if only one is listed, the other is obvious, and a 3-4 device fs with only one or two previous device changes, likely well remembered by the admin, should still be reasonably easy to guess), but as the number of devices and the number of device adds/removes/replaces increases, finding/guessing the missing one becomes far more difficult. Of course the sysadmin's first rule of backups states in simple form that not having one == defining the value of the data as trivial, not worth the trouble of a backup, which in turn means that at some point before there's /too/ many device change events, it's likely going to be less trouble (particularly after factoring in reliability) to restore from backups to a fresh filesystem than it is to do yet another device change, and together with the current practical limits btrfs imposes on the number of missing devices, that tends to impose /some/ limit on the possibilities for missing device IDs, so the situation, while not ideal, isn't yet /entirely/ out of hand, either, because a successful guess based on available information should be possible without /too/ many attempts. -- 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How to replace a failed drive in btrfs RAID 1 filesystem
09.03.2018 19:43, Austin S. Hemmelgarn пишет: > > If the answer to either one or two is no but the answer to three is yes, > pull out the failed disk, put in a new one, mount the volume degraded, > and use `btrfs replace` as well (you will need to specify the device ID > for the now missing failed disk, which you can find by calling `btrfs > filesystem show` on the volume). I do not see it and I do not remember ever seeing device ID of missing devices. 10:/home/bor # blkid /dev/sda1: UUID="ce0caa57-7140-4374-8534-3443d21f3edc" TYPE="swap" PARTUUID="d2714b67-01" /dev/sda2: UUID="cc072e56-f671-4388-a4a0-2ffee7c98fdb" UUID_SUB="eaeb4c78-da94-43b3-acc7-c3e963f1108d" TYPE="btrfs" PTTYPE="dos" PARTUUID="d2714b67-02" /dev/sdb1: UUID="e4af8f3c-8307-4397-90e3-97b90989cf5d" UUID_SUB="f421f1e7-2bb0-4a67-a18e-cfcbd63560a8" TYPE="btrfs" PARTUUID="875525bf-01" 10:/home/bor # mount /dev/sdb1 /mnt mount: /mnt: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error. 10:/home/bor # mount -o degraded /dev/sdb1 /mnt 10:/home/bor # btrfs fi sh /mnt Label: none uuid: e4af8f3c-8307-4397-90e3-97b90989cf5d Total devices 2 FS bytes used 256.00KiB devid2 size 1023.00MiB used 212.50MiB path /dev/sdb1 *** Some devices missing 10:/home/bor # btrfs fi us /mnt Overall: Device size: 2.00GiB Device allocated:425.00MiB Device unallocated:1.58GiB Device missing: 1023.00MiB Used:512.00KiB Free (estimated):912.62MiB (min: 912.62MiB) Data ratio: 2.00 Metadata ratio: 2.00 Global reserve: 16.00MiB (used: 0.00B) Data,RAID1: Size:102.25MiB, Used:128.00KiB /dev/sdb1 102.25MiB missing 102.25MiB Metadata,RAID1: Size:102.25MiB, Used:112.00KiB /dev/sdb1 102.25MiB missing 102.25MiB System,RAID1: Size:8.00MiB, Used:16.00KiB /dev/sdb1 8.00MiB missing 8.00MiB Unallocated: /dev/sdb1 810.50MiB missing 810.50MiB 10:/home/bor # rpm -q btrfsprogs btrfsprogs-4.15-2.1.x86_64 10:/home/bor # uname -a Linux 10 4.15.7-1-default #1 SMP PREEMPT Wed Feb 28 12:40:23 UTC 2018 (a36e160) x86_64 x86_64 x86_64 GNU/Linux 10:/home/bor # And "missing" is not the answer because I obviously may have more than one missing device. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How to replace a failed drive in btrfs RAID 1 filesystem
Austin S. Hemmelgarn wrote: On 2018-03-09 11:02, Paul Richards wrote: Hello there, I have a 3 disk btrfs RAID 1 filesystem, with a single failed drive. Before I attempt any recovery I’d like to ask what is the recommended approach? (The wiki docs suggest consulting here before attempting recovery[1].) The system is powered down currently and a replacement drive is being delivered soon. Should I use “replace”, or “add” and “delete”? Once replaced should I rebalance and/or scrub? I believe that the recovery may involve mounting in degraded mode. If I do this, how do I later get out of degraded mode, or if it’s automatic how do i determine when I’m out of degraded mode? It won't automatically mount degraded, you either have to explicitly ask it to, or you have to have an option to do so in your default mount options for the volume in /etc/fstab (which is dangerous for multiple reasons). Now, as to what the best way to go about this is, there are three things to consider: 1. Is the failed disk still usable enough that you can get good data off of it in a reasonable amount of time? If you're replacing the disk because of a lot of failed sectors, you can still probably get data off of it, while something like a head crash isn't worth trying to get data back. 2. Do you have enough room in the system itself to add another disk without removing one? 3. Is the replacement disk at least as big as the failed disk? If the answer to all three is yes, then just put in the new disk, mount the volume normally (you don't need to mount it degraded if the failed disk is working this well), and use `btrfs replace` to move the data. This is the most efficient option in terms of both time and is also generally the safest (and I personally always over-spec drive-bays in systems we build where I work specifically so that this approach can be used). If the answer to the third question is no, put in the new disk (removing the failed one first if the answer to the second question is no), mount the volume (mount it degraded if one of the first two questions is no, normally otherwise), then add the new disk to the volume with `btrfs device add` and remove the old one with `btrfs device delete` (using the 'missing' option if you had to remove the failed disk). This is needed because the replace operation requires the new device to be at least as big as the old one. If the answer to either one or two is no but the answer to three is yes, pull out the failed disk, put in a new one, mount the volume degraded, and use `btrfs replace` as well (you will need to specify the device ID for the now missing failed disk, which you can find by calling `btrfs filesystem show` on the volume). In the event that the replace operation refuses to run in this case, instead add the new disk to the volume with `btrfs device add` and then run `btrfs device delete missing` on the volume. If you follow any of the above procedures, you don't need to balance (the replace operation is equivalent to a block level copy and will result in data being distributed exactly the same as it was before, while the delete operation is a special type of balance), and you generally don't need to scrub the volume either (though it may still be a good idea). As far as getting back from degraded mode, you can just remount the volume to do so, though I would generally suggest rebooting. Note that there are three other possible approaches to consider as well: 1. If you can't immediately get a new disk _and_ all the data will fit on the other two disks, use `btrfs device delete` to remove the failed disk anyway, and run with just the two until you can get a new disk. This is exponentially safer than running the volume degraded until you get a new disk, and is the only case you realistically should delete a device before adding the new one. Make sure to balance the volume after adding the new device. 2. Depending on the situation, it may be faster to just recreate the whole volume from scratch using a backup than it is to try to repair it. This is actually the absolute safest method of handling this situation, as it makes sure that nothing from the old volume with the failed disk causes problems in the future. 3. If you don't have a backup, but have some temporary storage space that will fit all the data from the volume, you could also use `btrfs restore` to extract files from the old volume to temporary storage, recreate the volume, and copy the data back in from the temporary storage. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html I did a quick scan of the wiki just to see, but I did not find any good info about how to recover a "RAID" like set if degraded. Information about how to recover, and what profiles can be recovered from would be good to have
Re: How to replace a failed drive in btrfs RAID 1 filesystem
On 2018-03-09 11:53, Paul Richards wrote: Fantastic response! Thank you. I haven’t investigated how broken the failed drive is, I just shutdown as soon as I noticed. The 3 drives were 8, 8 and 2 TB. The 2TB one failed and I’m replacing it with a new 8TB. So the new drive is indeed larger. If I do a “replace” I’ll end up with the same block distribution as before, so would likely want to balance afterwards. Yes, you probably do, but you'll also need to resize the device first (which I forgot to mention in my reply), as replace doesn't expand that part of the volume to fill the new device. I think, but I’ll need to confirm, that I have enough free space to do a mount degraded, delete, remount non-degraded again, then add, and rebalance. This will leave me in degraded mode for the shortest time if my understanding is correct. Assuming you can fit all the data on the two 8TB drives, then yes this will result int he shortest amount of time running degraded (although, if the failed drive is mostly working, you may not need to mount degraded at all to do this), though keep in mind that this will also result in significant load on the other disks and will give you degraded performance for the longest amount of time. Thanks again for your notes, they should be on the wiki.. :) I've been meaning to add it for a while actually, I just haven't gotten around to it yet. On Fri, 9 Mar 2018 at 16:43, Austin S. Hemmelgarn> wrote: On 2018-03-09 11:02, Paul Richards wrote: > Hello there, > > I have a 3 disk btrfs RAID 1 filesystem, with a single failed drive. > Before I attempt any recovery I’d like to ask what is the recommended > approach? (The wiki docs suggest consulting here before attempting > recovery[1].) > > The system is powered down currently and a replacement drive is being > delivered soon. > > Should I use “replace”, or “add” and “delete”? > > Once replaced should I rebalance and/or scrub? > > I believe that the recovery may involve mounting in degraded mode. If > I do this, how do I later get out of degraded mode, or if it’s > automatic how do i determine when I’m out of degraded mode? > It won't automatically mount degraded, you either have to explicitly ask it to, or you have to have an option to do so in your default mount options for the volume in /etc/fstab (which is dangerous for multiple reasons). Now, as to what the best way to go about this is, there are three things to consider: 1. Is the failed disk still usable enough that you can get good data off of it in a reasonable amount of time? If you're replacing the disk because of a lot of failed sectors, you can still probably get data off of it, while something like a head crash isn't worth trying to get data back. 2. Do you have enough room in the system itself to add another disk without removing one? 3. Is the replacement disk at least as big as the failed disk? If the answer to all three is yes, then just put in the new disk, mount the volume normally (you don't need to mount it degraded if the failed disk is working this well), and use `btrfs replace` to move the data. This is the most efficient option in terms of both time and is also generally the safest (and I personally always over-spec drive-bays in systems we build where I work specifically so that this approach can be used). If the answer to the third question is no, put in the new disk (removing the failed one first if the answer to the second question is no), mount the volume (mount it degraded if one of the first two questions is no, normally otherwise), then add the new disk to the volume with `btrfs device add` and remove the old one with `btrfs device delete` (using the 'missing' option if you had to remove the failed disk). This is needed because the replace operation requires the new device to be at least as big as the old one. If the answer to either one or two is no but the answer to three is yes, pull out the failed disk, put in a new one, mount the volume degraded, and use `btrfs replace` as well (you will need to specify the device ID for the now missing failed disk, which you can find by calling `btrfs filesystem show` on the volume). In the event that the replace operation refuses to run in this case, instead add the new disk to the volume with `btrfs device add` and then run `btrfs device delete missing` on the volume. If you follow any of the above procedures, you don't need to balance (the replace operation is equivalent to a block level copy and will result in data being distributed exactly the same as it was before, while the delete operation is a special type of balance), and you generally don't need to scrub
Re: How to replace a failed drive in btrfs RAID 1 filesystem
On 2018-03-09 11:02, Paul Richards wrote: Hello there, I have a 3 disk btrfs RAID 1 filesystem, with a single failed drive. Before I attempt any recovery I’d like to ask what is the recommended approach? (The wiki docs suggest consulting here before attempting recovery[1].) The system is powered down currently and a replacement drive is being delivered soon. Should I use “replace”, or “add” and “delete”? Once replaced should I rebalance and/or scrub? I believe that the recovery may involve mounting in degraded mode. If I do this, how do I later get out of degraded mode, or if it’s automatic how do i determine when I’m out of degraded mode? It won't automatically mount degraded, you either have to explicitly ask it to, or you have to have an option to do so in your default mount options for the volume in /etc/fstab (which is dangerous for multiple reasons). Now, as to what the best way to go about this is, there are three things to consider: 1. Is the failed disk still usable enough that you can get good data off of it in a reasonable amount of time? If you're replacing the disk because of a lot of failed sectors, you can still probably get data off of it, while something like a head crash isn't worth trying to get data back. 2. Do you have enough room in the system itself to add another disk without removing one? 3. Is the replacement disk at least as big as the failed disk? If the answer to all three is yes, then just put in the new disk, mount the volume normally (you don't need to mount it degraded if the failed disk is working this well), and use `btrfs replace` to move the data. This is the most efficient option in terms of both time and is also generally the safest (and I personally always over-spec drive-bays in systems we build where I work specifically so that this approach can be used). If the answer to the third question is no, put in the new disk (removing the failed one first if the answer to the second question is no), mount the volume (mount it degraded if one of the first two questions is no, normally otherwise), then add the new disk to the volume with `btrfs device add` and remove the old one with `btrfs device delete` (using the 'missing' option if you had to remove the failed disk). This is needed because the replace operation requires the new device to be at least as big as the old one. If the answer to either one or two is no but the answer to three is yes, pull out the failed disk, put in a new one, mount the volume degraded, and use `btrfs replace` as well (you will need to specify the device ID for the now missing failed disk, which you can find by calling `btrfs filesystem show` on the volume). In the event that the replace operation refuses to run in this case, instead add the new disk to the volume with `btrfs device add` and then run `btrfs device delete missing` on the volume. If you follow any of the above procedures, you don't need to balance (the replace operation is equivalent to a block level copy and will result in data being distributed exactly the same as it was before, while the delete operation is a special type of balance), and you generally don't need to scrub the volume either (though it may still be a good idea). As far as getting back from degraded mode, you can just remount the volume to do so, though I would generally suggest rebooting. Note that there are three other possible approaches to consider as well: 1. If you can't immediately get a new disk _and_ all the data will fit on the other two disks, use `btrfs device delete` to remove the failed disk anyway, and run with just the two until you can get a new disk. This is exponentially safer than running the volume degraded until you get a new disk, and is the only case you realistically should delete a device before adding the new one. Make sure to balance the volume after adding the new device. 2. Depending on the situation, it may be faster to just recreate the whole volume from scratch using a backup than it is to try to repair it. This is actually the absolute safest method of handling this situation, as it makes sure that nothing from the old volume with the failed disk causes problems in the future. 3. If you don't have a backup, but have some temporary storage space that will fit all the data from the volume, you could also use `btrfs restore` to extract files from the old volume to temporary storage, recreate the volume, and copy the data back in from the temporary storage. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html