Dear all, I understood better now how to compute a real available size and the total size on an Ext3 Fs Indeed in statfs or df, you have three field: f_blocks f_bfree f_bavail The difference between f_blocks and f_bfree is approximatively the size of the journal with some more information. The difference between f_bavail and f_bfree is the reserved space used to maintain the filesystem ( -m options approx 5%by default). So if you want to be safe and know the size available, use f_bavail and if you want to know the max size, add a "du -sh folder" result. Best regards. Stephane -----Original Message----- From: Andreas Dilger [mailto:adilger@xxxxxxxxx] Sent: lundi 7 février 2011 17:31 To: Stephane Cerveau Cc: ext3-users@xxxxxxxxxx Subject: Re: Compute the real total size of a partition formated in EXT3 On 2011-02-07, at 06:45, Stephane Cerveau wrote: > In order to have a real percentage of freespace for a user interface, I'm trying to compute the size available on a 4GB USB key formatted in Ext3. Indeed after format, when I ask df to give a summary of size, it tells that there is 75MB already used. > I would like to know the meaning of this 75MB ( is it the journal??) and especially how I can compute this when I want, whithout parsing the partition and the size of the file(s). > /dev/sda1 3.7G 71.5MB 3.4G 2% /mnt/internal There are several different things that add up to this overhead. The journal is a significant factor for smaller filesystems, but there are also inode tables, allocation bitmaps, reserved space, and a few other things. If you are using a very small embedded filesystem that doesn't need a lot of performance, you can reduce the size of the journal at format time with options like "-J size=4", and disable resizing with "-O ^resize_inode", which also removes some overhead. The amount of reserved space can be reduced with "-m <percentage>" (default 5%), though this can lead to significant file fragmentation and permanent performance impact. Finally, depending on your workload/usage pattern, the number of the inodes in the filesystem can be reduced using "-i <ratio>". As for computing the available size, you can't really do better than what statfs() returns. Cheers, Andreas __________ Information from ESET NOD32 Antivirus, version of virus signature database 5853 (20110207) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 5855 (20110208) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com _______________________________________________ Ext3-users mailing list Ext3-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/ext3-users
