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Background

I have a Synology NAS drive with two 2TB drives in a mirror configuration. I have run out of space so bought a HP Proliant Microserver N40L.

I have one spare 2TB so my aim was to install the 2TB drive on the Microserver, copy all my data from the Synology and then remove the 2x2TB from the Synology and install on the Microserver.

This would give me plenty of space, with room for expansion.

However, I've run out of space on the Microserver whilst copying all my data across which I can't get my head around.

The Synology and Microserver are both using ext3. Plus the synology has to use some of the disk for the OS. The Microserver comes with a 250GB and I've got my Ubuntu installation on that, so in theory I should have more storage on the Microserver 2TB than the Synology 2TB mirror.

Executing df -k on the HP Ubuntu system gives

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdb1 235662852 9007248 214858512 5% /
udev 3982948 4 3982944 1% /dev
tmpfs 1609884 1324 1608560 1% /run
none 5120 0 5120 0% /run/lock
none 4024708 272 4024436 1% /run/shm
/dev/sda1 1922859824 1825184256 0 100% /media/volume1

sda1 is my 2TB drive. As you can see it states 0 available.

Yet total blocks 1922859824 minus used blocks 1825184256 is 97675568.

So shouldn't I have around 100GB storage left?

After a bit of research I've tracked down the problem.

Actually two things were using up my disc space.

Firstly, the 2TB drive on my new setup had been created with the default ratio of inodes. For a 2TB drive this amounted to 122101760 inodes each of size 256k. As my drive is only going to used to store quite big media files, not large numbers of small files which is typical on a system disc, this default number of inodes is way too generous for the type of use the disc is being put to and taking up space I could use.

Unfortunately, the number of inodes can only be set when creating the partition and not altered afterwards.

The number of inodes is specified by the -N option on the make2fs command.

Second was the amount of space reserved for privileged processes on the partition. This is set to 5% by default. Again as my drive is going to be used to store media only and not system files I could reduce this to 0%.

The percentage reserved can be altered using the command

tune2fs -m X /dev/sda1

where X is the percentage you want reserved.

This can be altered after partition creation.

Hope this information helps others.