I answer mySelf: exporting NBD image file in copy-on-write mode, and starting several clients at the same time I can see that diff file is only 4096 bytes long ( the size of backing device bcache superblock) and seems not to increase size. So I can continue working with bcache :-) Thanks for your time. Cheers Juan Antonio El mié, 26-02-2014 a las 09:31 +0100, Juan Antonio Martinez escribió: > El mar, 25-02-2014 a las 11:37 -0500, Paul Clements escribió: > > On Tue, Feb 25, 2014 at 9:40 AM, Juan Antonio Martinez > > <jantonio@xxxxxxxxxx> wrote: > > > Hi all > > > (This is my first post on this list. I'm still a novice on bcache and > > > proper nettiquete on this list, so apologize for my mistakes) > > > Scenario: several NBD LTSP Fat Clients on (a bit) obsolete hardware > > > kernel 3.11.0-15 on Ubuntu 13.10 > > > /dev/sda1 as local cache device > > > /dev/nbd1 as remote NBD backing bcache device > > > - I've created and registered /dev/sda1 as cache device without problems > > > - To create nbd file to be exported I've typed following sequence: > > > # create an empty file > > > root# dd if=/dev/zero of=bcache_test.img bs=1M count=64 > > > # use it as loop block device > > > root# losetup /dev/loop0 > > > # make it a backing bcache device > > > root# make-bcache -B /dev/loop0 > > > have you tried doing this step from the client machine instead, i.e.: > > make-bache -B /dev/nbd1 > > after the nbd connection is up? does that work? > > Just tested: works fine.... but only in the LTSP client where I did the > changes, and had to tell nbd-server to export imagefile in read-write > mode > > Remember that my configuration consist in several (>250!) LTSP-NBD > clients sharing _the_same_ mounted squashfs image file. I cannot for > obious reasons make the image file to be shared read-write on every > clients at the same time... and seems that bcache needs write access to > the backing block device to work > > ¿Is this correct? If so, bcache is not for me :-( ¿Any alternatives? > > Perhaps I coult try to create bcache'd image file, and then modify NBD > server permissions to export in copy-on-write-mode... but this would > work if bcache only writes in bcache superblock ( my image files are > typically 8Gb size each) as this will create one cow file per client on > server > > Cheers > Juan Antonio -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
