1 |
On 7 November 2011, at 19:32, Michael Mol wrote: |
2 |
|
3 |
> On Mon, Nov 7, 2011 at 2:26 PM, Alan McKinnon <alan.mckinnon@×××××.com> wrote: |
4 |
>> ext2/3/4 are all backwards compatible. ext4 does have a certain feature |
5 |
>> (I forget what) that once used breaks this compatibility but you are |
6 |
>> highly, highly unlikely to ever do that on /boot. |
7 |
> |
8 |
> "Extents," I believe. But I don't know exactly what that means, or |
9 |
> when it comes into play. |
10 |
|
11 |
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). |
12 |
|
13 |
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. |
14 |
|
15 |
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. |
16 |
|
17 |
Stroller. |
18 |
|
19 |
|
20 |
|
21 |
|
22 |
[1] http://en.wikipedia.org/wiki/Ext4#Features |
23 |
[2] http://computer-forensics.sans.org/blog/2011/03/28/digital-forensics-understanding-ext4-part-3-extent-trees |