[Dirvish] Replacing backup drive
jconger at foobox.com
Sat Jul 14 13:34:30 UTC 2018
On 07/14/2018 08:46 AM, Rich Shepard wrote:
> Very interesting. I've not needed to learn about inodes before. Thank you.
Wiki has a good summary of the inode,
https://en.wikipedia.org/wiki/Inode. Every file is has an inode. The
inode is the head of the file, it has all the meta data that is not part
of the file like ownership and dates as well as the link to where the
file is on disk. Since drivish is collecting files from many source file
systems into one file system, you may need more inodes than normally
allocated in the backup file system. Some file systems create inodes on
the fly, some have a fixed number based on the file system create
options. You also need an inode for each version of the file over the
This is one of the reasons I use LVM volumes with individual file
systems for each host I am backing up. I backup five hosts over the
network and although I can survive all the files from all the file
systems on one source host in one backup file system, I didn't want to
put five hosts' worth of files into one file system. I've learned to
always keep some disk space in reserve so if a host's backup file system
is getting full, I can expand it. I also use LVM to join smaller drives
together and mirror across multiple drives.
What dirvish truly beats the snot out of is the directory storage. Say
you are keeping 30 days of snapshots. If a file hasn't changed in those
30 days, it is stored once using one inode -- but it is in 30
directories. If you are investigating file systems, which is a bit like
trying out religions, don't pick one with limited directory storage or
poor directory performance.
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