Re: BTRFS partition usage...

From: Jan Engelhardt
Date: Tue Feb 12 2008 - 10:05:05 EST


>
On Feb 12 2008 09:35, Chris Mason wrote:
>>
>> and slap the bootloader into "MBR", just like on x86.
>> Or I am missing something..
>
>It was a request from hpa, and he clearly had something in mind. He kindly
>offered to review the disk format for bootloaders and other lower level
>issues but I asked him to wait until I firm it up a bit.
>
>From my point of view, 0 is a bad idea because it is very likely to conflict
>with other things. There are lots of things in the FS that need deep
>thought,and the perfect system to fully use the first 64k of a 1TB filesystem
>isn't quite at the top of my list right now ;)
>
>Regardless of offset, it is a good idea to mop up previous filesystems where
>possible, and a very good idea to align things on some sector boundary. Even
>going 1MB in wouldn't be a horrible idea to align with erasure blocks on SSD.

I still don't like the idea of btrfs trying to be smarter than a user
who can partition up his system according to
(a) his likes
(b) system or hardware requirements or recommendations
to align the superblock to a specific location.

1MB alignment does not always mean 1MB alignment.
Sector 1 begins at 0x7e00 on x86.
And with the maximum CHS geometry (255/63), partitions begin
at 0x7e00+n*8225280 bytes, so the SB is unlikely to ever be on
a 1048576 boundary.
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