Dne 18.8.2015 v 08:45 Thiago Padilha napsal(a):
I need a device mapper target that stores data in files of fixed
sizes, probably defined when the virtual device is first created. For
the sake of explanation, lets call this target as "dirdm" and assume
there's an userspace tool of the same name that can be used to manage
such virtual devices. Now let's say I have an empty directory "/dirdm"
and want to create a virtual device with 4k "block size" on top of it:
dirdm create --size 10G --block-size 4k /dirdm
After this command is executed, there's a new file with 4k size at
/dirdm/0. This file will be used to store the first block of the
device. Here are the filenames that represent some blocks of this
virtual device:
Hi
I don't quite follow what you try to invent here - it looks like you play with
the idea of doing 'btrfs' without btrfs.
DM is about devices - as soon as you start to mix 'filesystem-layer' with
'block-layer' you get into troubles you cannot resolve - simply because of the
interacting locking inside kernel is not supported for this use-case.
i.e. for initial playing you could use any file via 'loop' device.
(There is even dm-loop support which however is not upstream since there
is already 'loop' target.)
At the end however you will get into cases you cannot resolve once your
filesystem on DM device will get blocked by underlying filesystem used to hold
backend file for loop device.
For DM - you should stay with pure block devices. Loop over filesystem is good
for 'testing' but it should be avoided as advised way for using any DM device.
For b-tree layered storage please check thin-pool.
Regards
Zdenek
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