Re: [gentoo-user] ext4/ext3 for /boot?

[Michael Mol]

On Mon, Nov 7, 2011 at 3:42 PM, Stroller <stroller@××××××××××××××××××.uk> wrote:
> On 7 November 2011, at 19:32, Michael Mol wrote:
>> On Mon, Nov 7, 2011 at 2:26 PM, Alan McKinnon <alan.mckinnon@×××××.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.


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:wq