Hi,
I know that bcache doesn't natively support multi-level caching but I
was playing with it and found this interesting "workaround":
make-bcache -B /dev/vdb -C /dev/vdc
the above command will generate a /dev/bcache0 device that we can now
use as backing (or cached) device:
make-bcache -B /dev/bcache0 -C /dev/vdd
This will make the kernel panic because the driver is trying to create
a duplicated "bcache" folder under /sys/block/bcache0/ .
So, simply patching the code inside register_bdev to create a folder
"bcache2" if "bcache" already exists does the trick.
Now I have:
vdb 252:16 0 5G 0 disk
└─bcache0 251:0 0 5G 0 disk
└─bcache1 251:128 0 5G 0 disk /mnt/bcache1
vdc 252:32 0 10G 0 disk
└─bcache0 251:0 0 5G 0 disk
└─bcache1 251:128 0 5G 0 disk /mnt/bcache1
vdd 252:48 0 5G 0 disk
└─bcache1 251:128 0 5G 0 disk /mnt/bcache1
Is anyone using this functionality? I assume not, because by default
it doesn't work.
Is there any good reason why this doesn't work by default?
I tried to understand how data will be read out of /dev/bcache1: will
the /dev/vdd cache, secondly created cache device, be interrogated
first and then will it be the turn of /dev/vdc ?
Meaning: can we consider that now the layer structure is
vdd
└─vdc
└─bcache0
└─bcache1
?
