Error while attaching a disk as readonly mode to multiple instances

[Vikram Singh Saggu]

We are attaching a disk (readonly-pipeline) as readonly mode to multiple instances. Some times it gives error while attaching to instances.

I am using a startup script to attach the "readonly-pipeline" disk as readonly mode to newly created instances

"readonly-pipeline" disk was already attached to 4 instances. On new instance bootup in my startupscript i am using a command to attach "readonly-pipeline" disk as readonly to multiple instances where it gave the below error message

Error Message

ERROR: RESOURCE_IN_USE_BY_ANOTHER_RESOURCE: The disk resource 'projects/XXXX/zones/us-central1-a/disk

s/readonly-pipeline' is already being used by 'projects/XXXX/zones/us-central1-a/instances/yg-as-sortedbam123'

[Omar KAMMOUN]

I have the same issue

gcloud compute instances attach-disk cp300-05-bis --disk cp-300-05-data --device-name data --mode ro

- The disk resource '******disks/cp-300-05-data' is already being used by '*****instances/cp300-05' 

[Vikram Singh Saggu]

Hi,

But now i do not get the error on attaching disk as read-only to multiple disk. Try below script.

#!/bin/bash

gcloud compute instances attach-disk instance-2 --disk example-disk-readonly --mode ro --zone europe-west1-c

sudo mkdir /mnt/sdb1

mount /dev/sda1 /mnt/sdb1

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Thanks ,

Vikram

[Omar KAMMOUN]

Thank you for your replay

I misunderstand the doc

I thought one can write and all other can read,

but it's actually, if one write no one read,
but if no one write, all can read

few test

#i already have an instance name instance-1 in us-central1-a zone

#default config so i don't have to set --zone evry time

#gcloud config set compute/region us-central1

gcloud config set compute/zone us-central1-a

#create disk my-ro-disk

gcloud compute disks create my-ro-disk --size 10GB

#attach disk my-ro-disk in read write mode

gcloud compute instances attach-disk instance-1 --disk my-ro-disk --device-name ro-disk

#SSH to instance-1 

gcloud compute ssh instance-1

# /!\ Prepare and FORMAT!!! disk for the first time, all data will be lost!

kammoun.o@instance-1:~$ sudo mkfs.ext4 -F /dev/disk/by-id/google-ro-disk

#Mount disk && create some content

kammoun.o@instance-1:~$ sudo mkdir /mnt/ro-disk

kammoun.o@instance-1:~$ sudo mount /dev/disk/by-id/google-ro-disk /mnt/ro-disk/

kammoun.o@instance-1:~$ sudo chmod 777 /mnt/ro-disk

kammoun.o@instance-1:~$ echo "Hello" > /mnt/ro-disk/hello.txt

#Unmount disk

kammoun.o@instance-1:~$ sudo umount /dev/disk/by-id/google-ro-disk

kammoun.o@instance-1:~$ exit

#Switch mode from rw to ro

gcloud compute instances detach-disk instance-1 --disk my-ro-disk

gcloud compute instances attach-disk instance-1 --disk my-ro-disk --device-name ro-disk --mode ro

#create new instance : instance-2

gcloud compute instances create instance-2 --machine-type f1-micro --image debian-8

#Attach disk in ro mode

gcloud compute instances attach-disk instance-2 --disk my-ro-disk --device-name ro-disk --mode ro

#SSH to instance-1 then Mount disk && check content

gcloud compute ssh instance-1

kammoun.o@instance-1:~$ sudo mount /dev/disk/by-id/google-ro-disk /mnt/ro-disk/

mount: /dev/sdb is write-protected, mounting read-only

kammoun.o@instance-1:~$ cat /mnt/ro-disk/hello.txt

Hello

kammoun.o@instance-1:~$ exit

#SSH to instance-2 then Mount disk && check content

gcloud compute ssh instance-2

kammoun.o@instance-1:~$ sudo mkdir /mnt/ro-disk

kammoun.o@instance-1:~$ sudo mount /dev/disk/by-id/google-ro-disk /mnt/ro-disk/

mount: /dev/sdb is write-protected, mounting read-only

kammoun.o@instance-1:~$ sudo chmod 777 /mnt/ro-disk

chmod: changing permissions of ‘/mnt/ro-disk’: Read-only file system

kammoun.o@instance-1:~$ cat /mnt/ro-disk/hello.txt

Hello

kammoun.o@instance-1:~$ exit