Re: dd between thin provisioned devices

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Dne 27.1.2013 11:01, devicemapper niko napsal(a):
Hi,everyone
if we dd between thin provisioned devices,
can we just get allocated blocks copied ?

Nope - devices mapper target operates on block level - not on the filesystem
level - so it has no knowledge about file layout.

What I could eventually imagine is some kind of block compactification (just like kernel does for hugepages) - but it's currently not being developed....


Will the output thin device get fully provisioned?
I glanced through the dm-thin code,
it turns out unmapped blocks return zeroed,am i right?

depends on settings - you could have either zeroed block or block
with content left on the disk - i.e. running thin with 1MB block/chunk size
means - before the first use whole 1MB must be zeroed - so it has its price.

Is there a trick to tell upper applications that all u got are zeroes.
or should they scan zeroed blocks themselves to trigger WRITE_SAME to reduce
I/O load?


Documentation/device-mapper/thin-provisioning.txt
see flag: skip_block_zeroing

Eventually for lvm2   lvcreate --zero y|n for thin pool creation.

Zdenek

--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel


[Index of Archives]     [DM Crypt]     [Fedora Desktop]     [ATA RAID]     [Fedora Marketing]     [Fedora Packaging]     [Fedora SELinux]     [Yosemite Discussion]     [KDE Users]     [Fedora Docs]

  Powered by Linux