To resolve the slow guest I/O performance and unmap failures.
Symptoms:
- In ESXi 6.7 U2 or later Linux VMs fails unmap and windows VMs can hang or have slow IO performance
- After deleting the snapshot and doing a rescan in Linux VMs the DISC-MAX SIZE is 32M.
- After creating a snapshot, rebooting the VM the DISC-MAX size is 2G
- Once the snapshot is deleted and unmap is tried, the Linux Guest OS logs in /var/log/messages will show similar entries
May 8 23:08:25 promb-gen-dhcp33 kernel: [ 3654.168449] sd 2:0:1:0: [sdb] tag#0 Send: scmd 0x00000000a4fc20d0
May 8 23:08:25 promb-gen-dhcp33 kernel: [ 3654.168450] sd 2:0:1:0: [sdb] tag#0 CDB: Unmap/Read sub-channel 42 00 00 00 00 00 00 00 18 00
May 8 23:08:25 promb-gen-dhcp33 kernel: [ 3654.168491] sd 2:0:1:0: [sdb] tag#0 Done: ADD_TO_MLQUEUE Result: hostbyte=DID_OK driverbyte=DRIVER_OK
May 8 23:08:25 promb-gen-dhcp33 kernel: [ 3654.168509] sd 2:0:1:0: [sdb] tag#0 CDB: Unmap/Read sub-channel 42 00 00 00 00 00 00 00 18 00
May 8 23:08:25 promb-gen-dhcp33 kernel: [ 3654.168511] sd 2:0:1:0: [sdb] tag#0 scsi host busy 1 failed 0
May 8 23:08:25 promb-gen-dhcp33 kernel: [ 3654.168512] sd 2:0:1:0: [sdb] tag#0 Inserting command 00000000a4fc20d0 into mlqueue
- Running this command time fstrim -av provides below output
fstrim: /mnt/sdb: FITRIM ioctl failed: Input/output error
- In case of Windows, VM slows down after migration from VVol to VMFS6 or vice-versa causing Windows VM to hang , slow IO performance and frequent VSCSI resets.
- Latency is not seen on esxtop from datastore view "u" or VM view "v"
Note:The preceding log excerpts are only examples.Date,time and environmental variables may vary depending on your environment.