eio and loop devices

[mehryari]

Any idea how I can use eio_cli for caching utilizing a loop device like ramdisk? udev rules creation fails during the driver construction.

Any hint will be greatly appreciated,

[bhansaliakhil]

Hello Mehryari,

The problem with loop-device is, they do not have UID associated with them. Hence cache created using loop device will not be persistent across reboot. So as you create cache using them, it does not fail, it fails to create corresponding udev rule file.

Here are sequence of steps for your reference which will allow you to create cache however I would not recommend you to do so. Thanks.

1. losetup /dev/loop0 /mnt2/mydev
   Creates loop device for file /mnt2/mydev.
2. [root@eiodev-01 mnt2]# eio_cli create -d /dev/loop0 -s /dev/sdc1 -p fifo -m wt -b 4096 -c c1
   Cache Name : c1
   Source Device : /dev/loop0
   SSD Device : /dev/sdc1
   Policy : fifo
   Mode : Write Through
   Block Size : 4096
   Associativity : 256
   None
   ENV{ID_SERIAL}=="36d4ae520b3482a001acd3e290b901ace", ATTR{partition}=="1"
   Creation of udev rules file failed

expected a character buffer object
Cache created successfully

1. [root@eiodev-01 mnt2]# eio_cli info
   Cache Name : c1
   Source Device : /dev/loop0
   SSD Device : /dev/sdc1
   Policy : fifo
   Mode : Write Through
   Block Size : 4096
   Associativity : 256
   State : normal

You may perform I/O as well; however after reboot this cache will not persist!

Hope this helps!

~Akhil