Re: [REGRESSION] LVM-on-LVM: error while submitting device barriers

[Goffredo Baroncelli <kreijack@inwind.it>]

On 29/02/2024 21.22, Patrick Plenefisch wrote:
> On Thu, Feb 29, 2024 at 2:56 PM Goffredo Baroncelli <kreijack@inwind.it> wrote:
>>
>>> Your understanding is correct. The only thing that comes to my mind to
>>> cause the problem is asymmetry of the SATA devices. I have one 8TB
>>> device, plus a 1.5TB, 3TB, and 3TB drives. Doing math on the actual
>>> extents, lowerVG/single spans (3TB+3TB), and
>>> lowerVG/lvmPool/lvm/brokenDisk spans (3TB+1.5TB). Both obviously have
>>> the other leg of raid1 on the 8TB drive, but my thought was that the
>>> jump across the 1.5+3TB drive gap was at least "interesting"
>>
>>
>> what about lowerVG/works ?
>>
> 
> That one is only on two disks, it doesn't span any gaps

Sorry, but re-reading the original email I found something that I missed before:

> BTRFS error (device dm-75): bdev /dev/mapper/lvm-brokenDisk errs: wr
> 0, rd 0, flush 1, corrupt 0, gen 0
> BTRFS warning (device dm-75): chunk 13631488 missing 1 devices, max
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> tolerance is 0 for writable mount
> BTRFS: error (device dm-75) in write_all_supers:4379: errno=-5 IO
> failure (errors while submitting device barriers.)

Looking at the code, it seems that if a FLUSH commands fails, btrfs
considers that the disk is missing. The it cannot mount RW the device.

I would investigate with the LVM developers, if it properly passes
the flush/barrier command through all the layers, when we have an
lvm over lvm (raid1). The fact that the lvm is a raid1, is important because
a flush command to be honored has to be honored by all the
devices involved.


> 
>> However yes, I agree that the pair of disks involved may be the answer
>> of the problem.
>>
>> Could you show us the output of
>>
>> $ sudo pvdisplay -m
>>
>>
> 
> I trimmed it, but kept the relevant bits (Free PE is thus not correct):
> 
> 
>    --- Physical volume ---
>    PV Name               /dev/lowerVG/lvmPool
>    VG Name               lvm
>    PV Size               <3.00 TiB / not usable 3.00 MiB
>    Allocatable           yes
>    PE Size               4.00 MiB
>    Total PE              786431
>    Free PE               82943
>    Allocated PE          703488
>    PV UUID               7p3LSU-EAHd-xUg0-r9vT-Gzkf-tYFV-mvlU1M
> 
>    --- Physical Segments ---
>    Physical extent 0 to 159999:
>      Logical volume      /dev/lvm/brokenDisk
>      Logical extents     0 to 159999
>    Physical extent 160000 to 339199:
>      Logical volume      /dev/lvm/a
>      Logical extents     0 to 179199
>    Physical extent 339200 to 349439:
>      Logical volume      /dev/lvm/brokenDisk
>      Logical extents     160000 to 170239
>    Physical extent 349440 to 351999:
>      FREE
>    Physical extent 352000 to 460026:
>      Logical volume      /dev/lvm/brokenDisk
>      Logical extents     416261 to 524287
>    Physical extent 460027 to 540409:
>      FREE
>    Physical extent 540410 to 786430:
>      Logical volume      /dev/lvm/brokenDisk
>      Logical extents     170240 to 416260
> 
> 
>    --- Physical volume ---
>    PV Name               /dev/sda3
>    VG Name               lowerVG
>    PV Size               <2.70 TiB / not usable 3.00 MiB
>    Allocatable           yes
>    PE Size               4.00 MiB
>    Total PE              707154
>    Free PE               909
>    Allocated PE          706245
>    PV UUID               W8gJ0P-JuMs-1y3g-b5cO-4RuA-MoFs-3zgKBn
> 
>    --- Physical Segments ---
>    Physical extent 0 to 52223:
>      Logical volume      /dev/lowerVG/single_corig_rimage_0_iorig
>      Logical extents     629330 to 681553
>    Physical extent 52224 to 628940:
>      Logical volume      /dev/lowerVG/single_corig_rimage_0_iorig
>      Logical extents     0 to 576716
>    Physical extent 628941 to 628941:
>      Logical volume      /dev/lowerVG/single_corig_rmeta_0
>      Logical extents     0 to 0
>    Physical extent 628942 to 628962:
>      Logical volume      /dev/lowerVG/single_corig_rimage_0_iorig
>      Logical extents     681554 to 681574
>    Physical extent 628963 to 634431:
>      Logical volume      /dev/lowerVG/single_corig_rimage_0_imeta
>      Logical extents     0 to 5468
>    Physical extent 634432 to 654540:
>      FREE
>    Physical extent 654541 to 707153:
>      Logical volume      /dev/lowerVG/single_corig_rimage_0_iorig
>      Logical extents     576717 to 629329
> 
>    --- Physical volume ---
>    PV Name               /dev/sdf2
>    VG Name               lowerVG
>    PV Size               <7.28 TiB / not usable 4.00 MiB
>    Allocatable           yes
>    PE Size               4.00 MiB
>    Total PE              1907645
>    Free PE               414967
>    Allocated PE          1492678
>    PV UUID               my0zQM-832Z-HYPD-sNfW-68ms-nddg-lMyWJM
> 
>    --- Physical Segments ---
>    Physical extent 0 to 0:
>      Logical volume      /dev/lowerVG/single_corig_rmeta_1
>      Logical extents     0 to 0
>    Physical extent 1 to 681575:
>      Logical volume      /dev/lowerVG/single_corig_rimage_1_iorig
>      Logical extents     0 to 681574
>    Physical extent 681576 to 687044:
>      Logical volume      /dev/lowerVG/single_corig_rimage_1_imeta
>      Logical extents     0 to 5468
>    Physical extent 687045 to 687045:
>      Logical volume      /dev/lowerVG/lvmPool_rmeta_0
>      Logical extents     0 to 0
>    Physical extent 687046 to 1049242:
>      Logical volume      /dev/lowerVG/lvmPool_rimage_0
>      Logical extents     0 to 362196
>    Physical extent 1049243 to 1056551:
>      FREE
>    Physical extent 1056552 to 1473477:
>      Logical volume      /dev/lowerVG/lvmPool_rimage_0
>      Logical extents     369506 to 786431
>    Physical extent 1473478 to 1480786:
>      Logical volume      /dev/lowerVG/lvmPool_rimage_0
>      Logical extents     362197 to 369505
>    Physical extent 1480787 to 1907644:
>      FREE
> 
>    --- Physical volume ---
>    PV Name               /dev/sdb3
>    VG Name               lowerVG
>    PV Size               1.33 TiB / not usable 3.00 MiB
>    Allocatable           yes (but full)
>    PE Size               4.00 MiB
>    Total PE              349398
>    Free PE               0
>    Allocated PE          349398
>    PV UUID               Ncmgdw-ZOXS-qTYL-1jAz-w7zt-38V2-f53EpI
> 
>    --- Physical Segments ---
>    Physical extent 0 to 0:
>      Logical volume      /dev/lowerVG/lvmPool_rmeta_1
>      Logical extents     0 to 0
>    Physical extent 1 to 349397:
>      Logical volume      /dev/lowerVG/lvmPool_rimage_1
>      Logical extents     0 to 349396
> 
> 
>    --- Physical volume ---
>    PV Name               /dev/sde2
>    VG Name               lowerVG
>    PV Size               2.71 TiB / not usable 3.00 MiB
>    Allocatable           yes
>    PE Size               4.00 MiB
>    Total PE              711346
>    Free PE               255111
>    Allocated PE          456235
>    PV UUID               xUG8TG-wvp0-roBo-GPo7-sbvn-aE7I-NAHU07
> 
>    --- Physical Segments ---
>    Physical extent 0 to 416925:
>      Logical volume      /dev/lowerVG/lvmPool_rimage_1
>      Logical extents     369506 to 786431
>    Physical extent 416926 to 437034:
>      Logical volume      /dev/lowerVG/lvmPool_rimage_1
>      Logical extents     349397 to 369505
>    Physical extent 437035 to 711345:
>      FREE
> 
> 
> Finally, I am not sure if it's relevant, but I did struggle to expand
> the raid1 volumes across gaps when creating this setup. I did file a
> bug about that, though I am not sure if it's relevant, as I removed
> integrity and cache for brokenDisk & lvmPool:
> https://gitlab.com/lvmteam/lvm2/-/issues/6
> 
> Patrick
> 

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