works here
what is your pveversion -v ?
the task log of the backup which failed
I have different versions (from 4.4-18 to 5.0-30) and they have the same situation. Erlier it worked properly but it started about 3 month ago.
Log for example:
INFO: starting new backup job: vzdump 102 --mailnotification failure --fullbackup 1 --maxfiles 3 --remove 1 --storage RAID --quiet 1 --mailto
monitoring@2017878.ru --compress lzo --node SPKRN-SV-HV01 --mode snapshot
INFO: doing full backup, because no backup found in last 1 day(s)
INFO: Starting Backup of VM 102 (qemu)
INFO: status = running
INFO: update VM 102: -lock backup
INFO: VM Name: SPKRN-SV-FS01
INFO: include disk 'scsi0' 'local:102/vm-102-disk-1.qcow2' 32G
INFO: include disk 'scsi1' 'local:102/vm-102-disk-2.qcow2' 150G
INFO: exclude disk 'scsi2' 'RAID:102/vm-102-disk-1.qcow2' (backup=no)
INFO: include disk 'scsi3' 'local:102/vm-102-disk-3.qcow2' 50G
INFO: include disk 'scsi4' 'local:102/vm-102-disk-4.qcow2' 32G
INFO: backup mode: snapshot
INFO: ionice priority: 7
INFO: creating archive '/var/lib/vz2/dump/vzdump-qemu-102-2018_04_01-21_00_02.vma.lzo'
INFO: started backup task 'e9e77ebe-3f15-4bb5-a43b-a181ed2035db'
INFO: status: 0% (642383872/283467841536), sparse 0% (145416192), duration 3, 214/165 MB/s
INFO: status: 1% (2968649728/283467841536), sparse 0% (246996992), duration 25, 105/101 MB/s
INFO: status: 2% (5695995904/283467841536), sparse 0% (276185088), duration 50, 109/107 MB/s
INFO: status: 3% (8518238208/283467841536), sparse 0% (362749952), duration 74, 117/113 MB/s
INFO: status: 4% (11450187776/283467841536), sparse 0% (444026880), duration 102, 104/101 MB/s
INFO: status: 5% (14174257152/283467841536), sparse 0% (485511168), duration 136, 80/78 MB/s
INFO: status: 6% (17017470976/283467841536), sparse 0% (515809280), duration 169, 86/85 MB/s
INFO: status: 7% (19864223744/283467841536), sparse 0% (534798336), duration 198, 98/97 MB/s
INFO: status: 8% (22707699712/283467841536), sparse 0% (580763648), duration 240, 67/66 MB/s
INFO: status: 9% (25564282880/283467841536), sparse 0% (634486784), duration 282, 68/66 MB/s
INFO: status: 10% (28381806592/283467841536), sparse 0% (674959360), duration 320, 74/73 MB/s
INFO: status: 11% (31252545536/283467841536), sparse 0% (689750016), duration 352, 89/89 MB/s
INFO: status: 12% (34050146304/283467841536), sparse 0% (700952576), duration 383, 90/89 MB/s
INFO: status: 13% (37027446784/283467841536), sparse 0% (707956736), duration 399, 186/185 MB/s
INFO: status: 14% (39700398080/283467841536), sparse 0% (755417088), duration 421, 121/119 MB/s
INFO: status: 15% (42530373632/283467841536), sparse 0% (759197696), duration 450, 97/97 MB/s
INFO: status: 16% (45402816512/283467841536), sparse 0% (759578624), duration 472, 130/130 MB/s
INFO: status: 17% (48266215424/283467841536), sparse 0% (762671104), duration 493, 136/136 MB/s
INFO: status: 18% (51087474688/283467841536), sparse 0% (766390272), duration 517, 117/117 MB/s
INFO: status: 19% (53952643072/283467841536), sparse 0% (766681088), duration 547, 95/95 MB/s
INFO: status: 20% (56719835136/283467841536), sparse 0% (767115264), duration 568, 131/131 MB/s
INFO: status: 21% (59555446784/283467841536), sparse 0% (777994240), duration 599, 91/91 MB/s
INFO: status: 22% (62439686144/283467841536), sparse 0% (810221568), duration 618, 151/150 MB/s
INFO: status: 23% (65213038592/283467841536), sparse 0% (833744896), duration 640, 126/124 MB/s
INFO: status: 24% (68050878464/283467841536), sparse 0% (833896448), duration 666, 109/109 MB/s
INFO: status: 25% (70875086848/283467841536), sparse 0% (833974272), duration 686, 141/141 MB/s
INFO: status: 26% (73748709376/283467841536), sparse 0% (835756032), duration 712, 110/110 MB/s
INFO: status: 27% (76614729728/283467841536), sparse 0% (836067328), duration 741, 98/98 MB/s
INFO: status: 28% (79438938112/283467841536), sparse 0% (836067328), duration 769, 100/100 MB/s
INFO: status: 29% (82244141056/283467841536), sparse 0% (839127040), duration 795, 107/107 MB/s
INFO: status: 30% (85112127488/283467841536), sparse 0% (883572736), duration 816, 136/134 MB/s
INFO: status: 31% (87973167104/283467841536), sparse 0% (883679232), duration 841, 114/114 MB/s
INFO: status: 32% (90792787968/283467841536), sparse 0% (885440512), duration 868, 104/104 MB/s
INFO: status: 33% (93665230848/283467841536), sparse 0% (886067200), duration 898, 95/95 MB/s
INFO: status: 34% (96441466880/283467841536), sparse 0% (888152064), duration 928, 92/92 MB/s
INFO: status: 35% (99216195584/283467841536), sparse 0% (888152064), duration 960, 86/86 MB/s
INFO: status: 36% (102161842176/283467841536), sparse 0% (894435328), duration 994, 86/86 MB/s
INFO: status: 37% (104887222272/283467841536), sparse 0% (899252224), duration 1023, 93/93 MB/s
INFO: status: 38% (107791908864/283467841536), sparse 0% (899428352), duration 1066, 67/67 MB/s
INFO: status: 39% (110558445568/283467841536), sparse 0% (901279744), duration 1113, 58/58 MB/s
INFO: status: 40% (113419091968/283467841536), sparse 0% (902184960), duration 1146, 86/86 MB/s
INFO: status: 41% (116309688320/283467841536), sparse 0% (905433088), duration 1177, 93/93 MB/s
INFO: status: 42% (119089594368/283467841536), sparse 0% (906354688), duration 1198, 132/132 MB/s
INFO: status: 43% (121935101952/283467841536), sparse 0% (906539008), duration 1221, 123/123 MB/s
INFO: status: 44% (124763111424/283467841536), sparse 0% (906657792), duration 1247, 108/108 MB/s
INFO: status: 45% (127610126336/283467841536), sparse 0% (906985472), duration 1275, 101/101 MB/s
INFO: status: 46% (130532179968/283467841536), sparse 0% (928133120), duration 1314, 74/74 MB/s
lzop: No space left on device: <stdout>
INFO: status: 46% (132319674368/283467841536), sparse 0% (950116352), duration 1335, 85/84 MB/s
ERROR: vma_queue_write: write error - Broken pipe
INFO: aborting backup job
ERROR: Backup of VM 102 failed - vma_queue_write: write error - Broken pipe
INFO: Backup job finished with errors
TASK ERROR: job errors