Am 27.06.2010 09:52, schrieb Shaochun Wang: > Hi: > > I want to tune my ext4 filesystem of NAS data partition to free its > reserved space by using "tune2fs -m0 <partition>". By reading the > manual of tune2fs, I observed the following words: > > "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. >
It's not meant for defragmentation but to avoid fragmentation in the first place. Simply speaking, as long as there is enough free space on the disk, even if it is not accessible by an ordinary user, the system can put new data in any place it seems fit. If the disk is really near 100% full, the system has to squeeze new data in every small hole somewhere on the disk. If this is done over a longer time, maybe by deleting files and creating new ones, it massively increases fragmentation. Besides, reserving some space for root can save your rear-end in case some user fills up your root partition. As long as root's processes still have a bit of disk space available, he can still log in and clean up the mess. I agree with you that reserving 5% of several TB is too much for these purposes. I think reducing it to a few 100MB is sufficient. Hope this helps, Florian Philipp
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