模拟已安装的卷错误以导致只读

Question

Few days ago we have encountered an unexpected error where one of the mounted drive on our RedHat linux machine became Read-Only. The issue was cause by the network outage in the datacenter.

Now I need to see if I can reproduce the same behavior where drive will be re-mounted as Read-Only while application is running.

I tried to remounted it was read-only but that didn't work because there are files that are opened (logs being written).

Is there a way to temporary cause the read-only if I have root access to the machine (but no access to the hypervisor).

That volume is mounted via /etc/fstab . Here is the record:

UUID=abfe2bbb-a8b6-4ae0-b8da-727cc788838f /                     ext4    defaults        1 1
UUID=8c828be6-bf54-4fe6-b68a-eec863d80133       /opt/sunapp     ext4    rw 0 2

Here are the output of few commands that shows details about our mounted drive. I can add more details as needed.

Output of fdisk -l

Disk /dev/vda: 268.4 GB, 268435456000 bytes, 524288000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0008ba5f

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048   524287966   262142959+  83  Linux

Disk /dev/vdb: 42.9 GB, 42949672960 bytes, 83886080 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Output of lsblk command:

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
vda    253:0    0   80G  0 disk 
└─vda1 253:1    0   80G  0 part /
vdb    253:16   0  250G  0 disk /opt/sunup

Output of blkid command:

/dev/vda1: UUID="abfe2bbb-a8b6-4ae0-b8da-727cc788838f" TYPE="ext4" 
/dev/sr0: UUID="2017-11-13-13-33-07-00" LABEL="config-2" TYPE="iso9660" 
/dev/vdb: UUID="8c828be6-bf54-4fe6-b68a-eec863d80133" TYPE="ext4" 

Output of parted -l command:

Warning: Unable to open /dev/sr0 read-write (Read-only file system).  /dev/sr0
has been opened read-only.
Error: /dev/sr0: unrecognised disk label
Model: QEMU QEMU DVD-ROM (scsi)                                           
Disk /dev/sr0: 461kB
Sector size (logical/physical): 2048B/2048B
Partition Table: unknown
Disk Flags: 

Model: Virtio Block Device (virtblk)
Disk /dev/vda: 268GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End    Size   Type     File system  Flags
 1      1049kB  268GB  268GB  primary  ext4         boot


Model: Virtio Block Device (virtblk)
Disk /dev/vdb: 42.9GB
Sector size (logical/physical): 512B/512B
Partition Table: loop
Disk Flags: 

Number  Start  End     Size    File system  Flags
 1      0.00B  42.9GB  42.9GB  ext4

Answer 1

Yes, you can do it. But the method proposed here may cause data loss, so use it only for testing.

Supposing you have /dev/vdb mounted as /opt/sunapp , do this:

1. First, unmount it. You may need to shut down any applications using it first.

2. Configure a loop device to mirror the contents of /dev/vdb :

    losetup /dev/loop0 /dev/vdb 

3. Then, mount /dev/loop0 instead of /dev/vdb :

    mount /dev/loop0 /opt/sunapp -o rw,errors=remount-ro 

4. Now, you can run your application. When it is time to make /opt/sunapp read-only, use this command:

    blockdev --setro /dev/vdb 

   After that, attempts to write to /dev/loop0 will result in I/O errors. As soon as file system driver detects this, it will remount the file system as read-only.

To restore everything back, you will need to unmount /opt/sunapp , detach the loop device, and make /dev/vdb writable again:

umount /opt/sunapp
losetup -d /dev/loop0
blockdev --setrw /dev/vdb

Answer 2

When I had some issues like corrupted disks, I had used ntfsfix. Please see if these commands, solve the problem.

sudo ntfsfix /dev/vda
sudo ntfsfix /dev/vdb