We're running various version of Ubuntu 14.04.2 LTS on Generation 2 Hyper-V Hosts.    On a random Basis, the file system will be mounted Read-Only due to a "disk error" (which really isn't the case here).    As a result, we must reboot the Ubuntu guest to get the file system to mount RW again.

The Error we see is the following:

Apr 30 00:02:01 balticnetworkstraining kernel: [640153.968142] storvsc: Sense Key : Unit Attention [current] 
Apr 30 00:02:01 balticnetworkstraining kernel: [640153.968145] storvsc: Add. Sense: Changed operating definition
Apr 30 00:02:01 balticnetworkstraining kernel: [640153.968161] sd 0:0:0:0: Warning! Received an indication that the operating parameters on this target have changed. The Linux SCSI layer does not automatically adjust these parameters.
Apr 30 01:23:26 balticnetworkstraining kernel: [645039.584164] hv_storvsc vmbus_0_4: cmd 0x2a scsi status 0x2 srb status 0x82
Apr 30 01:23:26 balticnetworkstraining kernel: [645039.584178] hv_storvsc vmbus_0_4: stor pkt ffff88006eb6c700 autosense data valid - len 18
Apr 30 01:23:26 balticnetworkstraining kernel: [645039.584180] storvsc: Sense Key : Unit Attention [current] 
Apr 30 01:23:26 balticnetworkstraining kernel: [645039.584183] storvsc: Add. Sense: Changed operating definition
Apr 30 01:23:26 balticnetworkstraining kernel: [645039.584198] sd 0:0:0:0: Warning! Received an indication that the operating parameters on this target have changed. The Linux SCSI layer does not automatically adjust these parameters.

This relates to the VSS "Windows Server Backup" process that kicks off at midnight on the host and finishes an hour and half later.   

Yes, we do have hv_vss_daemon and hv_kvp_daemon running for the correct kernel version we have.   We're currently running kernel version 3.13.0-49-generic #83 on one system and 3.16.0-34-generic #37 on the other. -- We see the same errors on both.

As a result, we've been hesitant to drop any more ubuntu guests on our 2012R2 hyper-v system because of this.   We can stop the backup process and all is good, but we need nightly backups to image all of our VM's.   All the windows guests have no issues of course.   We also have some CentOS based guests running without issues from what we've seen.

Any assistance would be great.

Brian

This failed write is definitely not expected. Can you tell me a little bit more about your environment, we'd like to replicate your conditions locally.

We're running as a host, a Supermicro 2U Server with Two E5-2690 Xeon CPU's, 8 cores each.   160GB of RAM and an adaptec 71605 16 port SATA RAID controller, with mostly all Samsung SSD's attached except for 4 WD 750GB Backup Disks.   These particular VM's are running on a block of 4 Raid 10 SSD's.   However, we've seen this issue on other host platforms we have with different configurations, so we've ruled out hardware as an issue.

Running Server 2012 R2 Datacenter, Version 6.3.9600.17196

Backup is standard Windows Server Backup to the dedicated Raid 10 Backup Set, nightly at midnight.   The VM guests are sitting on a standard NTFS file system.    The file system will mount ready-only randomly, but we usually see the problem once every 2-3 weeks...so it's not that often.  Regardless, I wouldn't expect this error to begin with.

Brian