VDI_IO_ERROR(Device I/O errors) when you run scheduled backup

olivierlambert

I suppose there's no timing correlation between both? Indeed, the error in xensource seems more meaningful, because it happens during the backup process.

shorian

Nothing in SMlog of interest at the point of backup. We only started looking there when hunting for any SR related issues, but I’m inclined to view it as ancillary. The SR exception doesn’t seem to be impacting day to day operations, whereas the CR item is a big concern for us, and now we’ve dug into it further there doesn’t seem to be a correlation between the two.

So...I agree with your synopsis and propose putting the SMlog’s exception to one side and we concentrate on the original issue - with the xensource.log error from my previous post.

Tomorrow I’m going to see if I can find a way of simulating a brief access delay it and see if that recreates the problem - I’ve seen something vaguely similar in some old Xen 6 bug reports and I’ve run out of anything sensible to try. Strangest thing is that it’s consistent across all of the boxes, and survives a fresh installation - which reminds me, I’ll also try it from and to an lvm target.

olivierlambert

Thanks. That's a weird issue anyway, eager to know if you have the same behavior with local LVM.

shorian

Initial test - looks like it's working fine running CR from EXT4 to LVM. I'm now doing a deep soak to increase confidence in that statement, but so far so good.

Good - in that it narrows down where we look. Bad - in that I need the thin provisioning, but pleased we've got some progress. Good shout @olivierlambert

shorian

Soak test running between two local hosts, ext4 -> lvm has worked faultlessly. I've now run 10 complete backups, without a single issue. Previous doing this ext4 > ext4 would have thrown errors maybe 25-50% of the time.

However running between two remote hosts. ext4 -> lvm over a 1gbps connection has hit the VDI_IO_ERROR issue

I'll try the reverse, lvm -> ext4. lvm -> lvm might be a challenge but I'll try and get something organised; to rearrange the boxes a little.

shorian

@olivierlambert Update after 20+ iterations - writing to lvm (ext4 -> lvm) between remote hosts has only failed 1/20 times which for me is more than acceptable, compared with writing ext4 -> ext4 which fails 80%.

Given when it did fail on lvm it was the same error, I think it's less likely to be the driver as the root cause, but instead a timing or back pressure issue? All the more so given that the issue only arose when writing to a remote (outside the firewall) host, but writing to a host inside the firewall has not had a single issue.

Also I think it's interesting that the issue was (largely) resolved by making the change at the target end, not the source, despite there not being much in the way of error logs at the point of failure on the target.

So....where to look next? Do you any tools that can simulate the above so we can enable / disable and therefore isolate the problem?

(Happy to allow you in via XOA if it makes life easier)

olivierlambert

It's really hard to track those random issues.

Sounds like a kind of race condition happening on your hardware/setup.

shorian

@olivierlambert So chances of resolving are minimal to none. Ugh. I'll keep digging around, it's proving a right pain in the @£$%

olivierlambert

Well, if you spot something or able to reproduce it easily with some protocol other people could try and also reproduce, that would increase the chances a lot

shorian

Some more insight - for past couple of weeks I've been running a CR backup simultaneously to two SRs on different boxes. One consistently fails (remote to an identical XCP-ng box, but over the web on a 1gbps link) with the usual error, but the other succeeds (inside the firewall, 1gbps link, identical XCP-ng box), which would point to the problem not being at the source but the use of a wide area transit.

So...here is SMlog at the time of the failure on the target:

SM: [24325] vdi_detach {'sr_uuid': 'cf2dbaa3-21f3-903b-0fd1-fbe68539f897', 'subtask_of': 'DummyRef:|b73e41cc-a667-4ac0-b0f9-545dcd88b08a|VDI.detach', 'vdi_ref': 'OpaqueRef:3c20a324-2c22-4977-a63e-5baee37f9372', 'vdi_on_boot': 'persist', 'args': [], 'o_direct': False, 'vdi_location': '923acf0b-03bf-44ba-a846-f468141910f3', 'host_ref': 'OpaqueRef:d1eeb523-7938-4d80-a465-68ba2f149846', 'session_ref': 'OpaqueRef:a73dd5d5-2115-4bff-9d56-5cec26e267d8', 'device_config': {'device': '/dev/disk/by-id/scsi-3600605b010276170276bb1850660dd94-part3', 'SRmaster': 'true'}, 'command': 'vdi_detach', 'vdi_allow_caching': 'false', 'sr_ref': 'OpaqueRef:0cb18a22-646b-4dab-b08e-21ca36628f62', 'local_cache_sr': 'cf2dbaa3-21f3-903b-0fd1-fbe68539f897', 'vdi_uuid': '923acf0b-03bf-44ba-a846-f468141910f3'}
SM: [24325] lock: opening lock file /var/lock/sm/923acf0b-03bf-44ba-a846-f468141910f3/vdi
SM: [24325] lock: released /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr
SM: [24380] lock: opening lock file /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr
SM: [24380] lock: acquired /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr
SM: [24380] ['/usr/sbin/td-util', 'query', 'vhd', '-vpfb', '/var/run/sr-mount/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/923acf0b-03bf-44ba-a846-f468141910f3.vhd']
SM: [24380]   pread SUCCESS
SM: [24380] vdi_delete {'sr_uuid': 'cf2dbaa3-21f3-903b-0fd1-fbe68539f897', 'subtask_of': 'DummyRef:|6236329b-d253-4da6-bc9b-d5498fd02069|VDI.destroy', 'vdi_ref': 'OpaqueRef:3c20a324-2c22-4977-a63e-5baee37f9372', 'vdi_on_boot': 'persist', 'args': [], 'o_direct': False, 'vdi_location': '923acf0b-03bf-44ba-a846-f468141910f3', 'host_ref': 'OpaqueRef:d1eeb523-7938-4d80-a465-68ba2f149846', 'session_ref': 'OpaqueRef:b8fbaaeb-221f-4956-9088-f8565ba34d0a', 'device_config': {'device': '/dev/disk/by-id/scsi-3600605b010276170276bb1850660dd94-part3', 'SRmaster': 'true'}, 'command': 'vdi_delete', 'vdi_allow_caching': 'false', 'sr_ref': 'OpaqueRef:0cb18a22-646b-4dab-b08e-21ca36628f62', 'local_cache_sr': 'cf2dbaa3-21f3-903b-0fd1-fbe68539f897', 'vdi_uuid': '923acf0b-03bf-44ba-a846-f468141910f3'}
SM: [24380] lock: unlinking lock file /var/lock/sm/923acf0b-03bf-44ba-a846-f468141910f3/vdi
SM: [24380] lock: removing lock dir /var/lock/sm/923acf0b-03bf-44ba-a846-f468141910f3
SM: [24380] lock: opening lock file /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/running
SM: [24380] lock: tried lock /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/running, acquired: True (exists: True)
SM: [24380] lock: released /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/running
SM: [24380] Kicking GC
SMGC: [24380] === SR cf2dbaa3-21f3-903b-0fd1-fbe68539f897: gc ===
SMGC: [24405] Will finish as PID [24406]
SMGC: [24380] New PID [24405]
SM: [24406] lock: opening lock file /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/running
SM: [24406] lock: opening lock file /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/gc_active
SM: [24406] lock: opening lock file /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr
SM: [24380] lock: released /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr
SMGC: [24406] Found 0 cache files
SM: [24406] lock: tried lock /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/gc_active, acquired: True (exists: True)
SM: [24406] lock: tried lock /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr, acquired: True (exists: True)
SM: [24406] ['/usr/bin/vhd-util', 'scan', '-f', '-m', '/var/run/sr-mount/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/*.vhd']
SM: [24406]   pread SUCCESS
SMGC: [24406] SR cf2d ('Xen12 SATA') (18 VDIs in 16 VHD trees):
SMGC: [24406]         b1392757(5.000G/1.589G)
SMGC: [24406]         *d1789c22(150.000G/87.188G)
SMGC: [24406]             71e7c935(150.000G/313.500K)
SMGC: [24406]             aae21e12(150.000G/1.218G)
SMGC: [24406]         7b458e2e(10.000G/3.106G)
SMGC: [24406]         0fd9483c(25.000G/15.661G)
SMGC: [24406]         ae6739bf(10.000G/4.730G)
SMGC: [24406]         d25b8134(20.000G/3.759G)
SMGC: [24406]         265ed8d8(150.000G/16.609G)
SMGC: [24406]         32474df8(100.000G/98.434G)
SMGC: [24406]         5ae3d2e6(50.000G/46.990G)
SMGC: [24406]         7fc5f335(250.000G/16.885G)
SMGC: [24406]         ba7c92a3(25.000G/15.661G)
SMGC: [24406]         d6de6348(20.000G/9.978G)
SMGC: [24406]         24c6b7e8(20.000G/9.978G)
SMGC: [24406]         ab433fff(50.000G/49.595G)
SMGC: [24406]         6750bf45(10.000G/3.704G)
SMGC: [24406]         f9e3cd7e(10.000G/5.949G)
SMGC: [24406]
SM: [24406] lock: released /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/sr
SMGC: [24406] Got sm-config for *d1789c22(150.000G/87.188G): {'vhd-blocks': 'eJzt1kESgiAUBmC5QTfgqB2Fq9QJOsKzCzTjqlooFakjkwjiQ5jm/xculHkf0MPUesil0zeNIAiCzOaa0T7rrhKBY4ld76pP3H7LLjr8Z2LI6Yv67cvEDLl9s/7UvjP9+nPx3v4L7PnoNk2x/7TKF13Z++8+mhzvhr7/FEOpSN+//rkQmy+ifK4M65fZfPEoYf35fHEqYv1NZj8wxOQOdYrZ/3/xxz5SrH7s5+Hd65vfX64qqszVPaVvNQopFbv/x9m7/ZSUDp6A5TcU+xZQv7fkdEZh/ups/wLZ//zZW5z//z+lT/4hpbz/1HCHFka7joc0V7sbl+qY58ryJ1FzVmCry7BhY3z9b8+iPVSsEb2/uU5mPzbw4cOHDx8+fPjw4cOHD38vv05U+QVg667e'}
SMGC: [24406] No work, exiting
SMGC: [24406] GC process exiting, no work left
SM: [24406] lock: released /var/lock/sm/cf2dbaa3-21f3-903b-0fd1-fbe68539f897/gc_active
SMGC: [24406] In cleanup
SMGC: [24406] SR cf2d ('Xen12 SATA') (18 VDIs in 16 VHD trees): no changes

The only thing I can see in there is the garbage collection.

Given that the issue seems to be something to do with the wide area network (same speed as inside the firewall, but obviously more hops), I wonder if this may be a similar problem as we're seeing in the S3 backups over the WAN? Could it be that some packets are being delayed in transit, or that there is an internal time limit on a backup chunk completing? Would also explain why backing up smaller VMs has a higher chance of success than the larger ones, since the % chance of a temporary timeout increases the longer a backup runs?

I've kept the set up as (finally) I now have 100% repeatability on the CR backup to the remote SR failure, so if someone wants to come in and have a look around it can be arranged. Others seem to have the same problem so hopefully this can help get to the root cause, as this the first time I've managed to get it to consistently fail every time. Appreciate that this doesn't sound like a success, but it beats an intermittent failure!

olivierlambert

Out of curiosity, can you do a: dmesg | grep -i cut -C10 (on your master host)

shorian

@olivierlambert Target or source?

olivierlambert

Try both.

shorian

Source:

# dmesg | grep -i cut -C10
[    0.000000] Xen: [mem 0x0000000079a66000-0x0000000079f6efff] ACPI NVS
[    0.000000] Xen: [mem 0x0000000079f6f000-0x000000008fffffff] reserved
[    0.000000] Xen: [mem 0x00000000c7ffc000-0x00000000c7ffcfff] reserved
[    0.000000] Xen: [mem 0x00000000fbffc000-0x00000000fbffcfff] reserved
[    0.000000] Xen: [mem 0x00000000fec00000-0x00000000fec01fff] reserved
[    0.000000] Xen: [mem 0x00000000fec40000-0x00000000fec40fff] reserved
[    0.000000] Xen: [mem 0x00000000fed1c000-0x00000000fed44fff] reserved
[    0.000000] Xen: [mem 0x00000000fee00000-0x00000000feefffff] reserved
[    0.000000] Xen: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
[    0.000000] Xen: [mem 0x0000000100000000-0x0000000270f0efff] usable
[    0.000000] NX (Execute Disable) protection: active
[    0.000000] SMBIOS 3.0 present.
[    0.000000] DMI: Supermicro X10DRi/X10DRi, BIOS 2.1 09/13/2016
[    0.000000] Hypervisor detected: Xen PV
[    0.047663] tsc: Fast TSC calibration using PIT
[    0.047664] tsc: Detected 2399.968 MHz processor
[    0.047665] tsc: Detected 2400.010 MHz TSC
[    0.049570] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[    0.049572] e820: remove [mem 0x000a0000-0x000fffff] usable
[    0.049578] last_pfn = 0x270f0f max_arch_pfn = 0x400000000
[    0.049579] Disabled

Target:

dmesg | grep -i cut -C10
[    0.000000] Xen: [mem 0x00000000fec10000-0x00000000fec10fff] reserved
[    0.000000] Xen: [mem 0x00000000fec18000-0x00000000fec18fff] reserved
[    0.000000] Xen: [mem 0x00000000fec20000-0x00000000fec20fff] reserved
[    0.000000] Xen: [mem 0x00000000fec28000-0x00000000fec28fff] reserved
[    0.000000] Xen: [mem 0x00000000fec30000-0x00000000fec30fff] reserved
[    0.000000] Xen: [mem 0x00000000fec38000-0x00000000fec38fff] reserved
[    0.000000] Xen: [mem 0x00000000fed20000-0x00000000fed44fff] reserved
[    0.000000] Xen: [mem 0x00000000fee00000-0x00000000feefffff] reserved
[    0.000000] Xen: [mem 0x00000000ff000000-0x00000000ffffffff] reserved
[    0.000000] Xen: [mem 0x0000000100000000-0x00000004a52a5fff] usable
[    0.000000] NX (Execute Disable) protection: active
[    0.000000] efi: EFI v2.50 by American Megatrends
[    0.000000] efi:  SMBIOS=0x6f0bc000  SMBIOS 3.0=0x6f0bb000  ACPI 2.0=0x6ca22000  ACPI=0x6ca22000  ESRT=0x64ba8f18
[    0.000000] SMBIOS 3.1.1 present.
[    0.000000] DMI: Supermicro SYS-6029P-TR/X11DPi-N, BIOS 2.0b 02/28/2018
[    0.000000] Hypervisor detected: Xen PV
[    0.000480] tsc: Detected 2200.030 MHz processor
[    0.002610] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[    0.002613] e820: remove [mem 0x000a0000-0x000fffff] usable
[    0.002624] last_pfn = 0x4a52a6 max_arch_pfn = 0x400000000
[    0.002625] Disabled

olivierlambert

Hmm nothing obvious here…

tuxen

This got my attention:

Jan 15 19:17:40 xcp-ng-xen12-lon2 xapi: [error||623653 INET :::80||import] Caught exception in import handler: VDI_IO_ERROR: [ Device I/O errors ]
Jan 15 19:17:40 xcp-ng-xen12-lon2 xapi: [error||623653 INET :::80||backtrace] VDI.import D:378e6880299b failed with exception Unix.Unix_error(Unix.EPIPE, "single_write", "")
Jan 15 19:17:40 xcp-ng-xen12-lon2 xapi: [error||623653 INET :::80||backtrace] Raised Unix.Unix_error(Unix.EPIPE, "single_write", "")

This Unix.EPIPE error on the remote target means that the pipe stream is being closed before VDI.Import receives all the data. The outcome is a VDI I/O error due to a broken, partial sent/received VDI.

Since a remote-over-the-internet link can be more prone to latency/intermittency issues, it might be needed to adjust the remote NFS soft timeout/retries or mounting the target with hard option.

I would also check if the remote target is running out-of-space during the backup process.

shorian

@tuxen Target has plenty of space, over 5Tb free or about 20x the cumulative VM sizes. No NFS involved, it’s a locally mounted ext4 raid 1 array on the target box.

If same backup takes place behind the firewall it runs successfully 95% of the time, across the WAN it fails 95% of the time. Both over a 1gbps link.

Sometimes the failures clean themselves up, sometimes end up with a VM/disk marked [importing.....<backup name><VM name>] that need to be manually removed.

Any help hugely appreciated.

olivierlambert

Interesting. It's like the data stream is interrupted somehow for a bit and that's enough to trigger the issue.

EddieCh08666741

i have similar issue like this too. I'm using ext4 and it was perfectly fine when i'm using 7.6. After upgrading to ext4 and 8.2 fresh install. The CR dont work anymore.

EddieCh08666741

I just tried installing Xen Orchestra from the sources on Debian 11. The same CR works well.

My previous Xen Orchestra from the sources ubuntu 18 having issue with VDI ERROR. Will do more testing.