On Mon, Nov 7, 2011 at 3:42 PM, Stroller <strol...@stellar.eclipse.co.uk> wrote: > On 7 November 2011, at 19:32, Michael Mol wrote: >> On Mon, Nov 7, 2011 at 2:26 PM, Alan McKinnon <alan.mckin...@gmail.com> >> wrote: >>> ext2/3/4 are all backwards compatible. ext4 does have a certain feature >>> (I forget what) that once used breaks this compatibility but you are >>> highly, highly unlikely to ever do that on /boot. >> >> "Extents," I believe. But I don't know exactly what that means, or >> when it comes into play. > > It means, as a huge simplification, that ext4 can allocate a file to blocks > 1234 - 1256, instead of having to separately allocate blocks 1234, 1235, > 1236, 1237, 1238, 1239, 1240, and so on (as ext3 would have had to do). > > This fixes ext3's "slow deletes" problem, because only a single entry in the > allocation table needs to be removed, instead of many. If you delete a big > file (say a 9gig DVD or 40gig blu-ray .iso image file) it's at least an order > of magnitude slower on ext3 than it is on ext4. > > As I said, this is a huge simplification, and I'm sure there are folks who > would take pleasure in explaining how wrong it is, but it's a good enough > explanation for a couple of sentences that you can easily grasp. For more > details the "Features - Extents" section of ext4's wikipedia page [1] and > this other article [2] (these are top hits on Google for "ext4 extents") look > pretty good. > > Stroller. > > [1] http://en.wikipedia.org/wiki/Ext4#Features > [2] > http://computer-forensics.sans.org/blog/2011/03/28/digital-forensics-understanding-ext4-part-3-extent-trees
Very, very nice reads. Thanks. -- :wq
