Re: The -c option of btrfs qgroup limit
Hi Koen, On 27.03.2013 00:36, Koen De Wit wrote: The btrfs qgroup limit command has an option -c which means limit amount of data after compression. Whether this option is specified or not, I seem to be able to write more well-compressible data than the specified limit. I was expecting that omitting the -c option would never allow me to write more data than specified by the limit. Am I missing something? Which difference in behavior should I expect from the -c option? Today: none. In the future: The one you describe. That option is planned but not implemented. We should have mentioned that in the qgroup usage, I agree. -Jan -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
The -c option of btrfs qgroup limit
Hello Koen, Although we offer '-c' option for btrfs qgroup limit, it has been not implemented yet. So until now, btrfs quota just limits the real space that writes to the space. Thanks, Wang -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
The -c option of btrfs qgroup limit
All, The btrfs qgroup limit command has an option -c which means limit amount of data after compression. Whether this option is specified or not, I seem to be able to write more well-compressible data than the specified limit. I was expecting that omitting the -c option would never allow me to write more data than specified by the limit. Am I missing something? Which difference in behavior should I expect from the -c option? Koen. --- This is what I did: Mount a btrfs filesystem with the compress option and turn on quota: # mkfs.btrfs -f /dev/sdg2 # mount -o compress /dev/sdg2 /mnt # cd /mnt # btrfs quota enable ./ Create a subvol and limit the amount of data after compression. Write some well-compressible files: # btrfs subvol create subvol1 # btrfs qgroup limit -c 3m ./subvol1 # for i in `seq 1 5`; do dd if=/dev/zero of=subvol1/file$i bs=1024 count=1000; sync; done (no errors) # du -s subvol1 5000 subvol1 We can write 5 MB of data to a file that is limited to 3 MB, which is normal in this case because data from /dev/zero is very good compressible. Create a subvol and limit the amount of data after compression. Write some poorly compressible files: # btrfs subvol create subvol2 # btrfs qgroup limit -c 3m ./subvol2 # for i in `seq 1 5`; do dd if=/dev/urandom of=subvol2/file$i bs=1024 count=1000; sync; done dd: writing `subvol2/file4': Disk quota exceeded dd: opening `subvol2/file5': Disk quota exceeded # du -s subvol2 3056 subvol2 Here we get quota violations, because data from /dev/urandom is poorly compressible. Now write some well-compressible data to a subvol that is limited without the -c option: # btrfs subvol create subvol3 # btrfs qgroup limit 3m ./subvol3 # for i in `seq 1 5`; do dd if=/dev/zero of=subvol3/file$i bs=1024 count=1000; sync; done (no errors) # du -s subvol3 5000 subvol3 We're still able to write 5 MB of data to a subvol that is limited to 3 MB. -- To unsubscribe from this list: send the line unsubscribe linux-btrfs in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
