On 27 Jun 2010, at 08:52, Shaochun Wang wrote:
... "Reserving some number of filesystem blocks for use by privileged processes is done to avoid filesystem fragmentation"It means that filesystem defragmentation need such reserved blocks to work properly, am I right? If so, can I make the reserved blocks a little because the default 5% is too much. My NAS filesystem is about 7x1.5T, then 5% means a lot of space.
I'm pretty sure that just means that Linux will try to put files in contiguous sectors, so they're not fragmented, and that as you run out of space it's generally harder to do that.
But I would imagine this is particularly the case with the occasional large file on a typical filesystem cluttered with small files - if you have a 1TB drive and save 9 100GB movie files on it, the remaining free space is going to be contiguous, anyway.
Whilst it would be interesting to do some real world testing on big hard drives fulla porn, you can safely set the reserved space to 0% and forget about it. That message has been there since ext2 and if you streaming suddenly starts to stutter when your filesystem is 99% full, well, you were going to add another drive to the array, anyway, weren't you? Add it in and expand the filesystem and see if that makes any difference.
Interestingly, I've just done an fsck on my ext4 media array and it shows as 83.8% non-contiguous. It is 1.4TB with 272G or 19% free. I can only assume this is because I also use it for backups, and have a couple of directories on there of many much smaller files.
Stroller.
