Clear the Disk Read-Only Flag in Windows

Clear the Disk Read-Only Flag in Windows

While recently adding a new disk to one of our backup servers, one of the disks changed device letters in Linux. Ordinarily this is not a big deal, but since this particular disk was a iblock device in an LIO backstore, and was defined by the /dev/sd[x] notation, it was no longer listed correctly. Oddly, the disk was still listed in the Disk Manager on the hypervisors, but any attempt at I/O would result in errors. The disk was ultimately removed from the LIO configuration, which then caused the LUN to drop from the hypervisor nodes.

After adding the disk back to LIO using a slicker method as detailed here, the disk reappeared on the hypervisors, and we reconnected the disk to the VM in Hyper-V. However, after adding the storage back, we noticed the LUN from LIO was marked as read-only in the virtual server, and would not permit any writes. Should you run into a similar situation, the fix is usually pretty simple, as noted below.

First, start the diskpart utility from a Windows CLI and list the available disks:


Next, select the disk in question, in this case Disk 6. Notice that when we look at the disk details in diskpart, this disk is definitely listed as read-only:


With the disk still selected, clear the readonly attribute for the disk with the following command:


The disk should now be listed as “Read-Only: No,” and available for writing. You can verify its status with the detail command as before.

We’re still not quite sure what caused this little issue, as we’ve removed and added several disks back in LIO without this cropping up. Perhaps it was the less than graceful removal of the disk from the hypervisor while it was attempting IO. Whatever the case, though an old utility, diskpart can still prove to be a useful tool when the need arises.

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