Dan McGhee wrote:
Yes it is but 100M is *way* too big. Note that for disks with 4K
sectors with 512 byte sector emulation, sector 34 above does not align
with the physical sector. It's not really that big a deal because it's
rarely written and only read at boot time.
See for instance
http://askubuntu.com/questions/201164/proper-alignment-of-partitions-on-an-advanced-format-hdd-using-parted
<http://askubuntu.com/questions/201164/proper-alignment-of-partitions-on-an-advanced-format-hdd-using-parted>
If it's done the same on all drives, then you don't need to worry about the
disk's physical format.
I've found on a virtual system like qemu, if I create a new GPT with gdisk, the
first sector is created at sector 2048 by default, which is a good standard to
use everywhere. parted doesn't do it right by default and the syntax is crazy.
The reason for Sector 34 on a GPT disk is that a GPT disk can hold
128 partitions. Each partition record is 128 bytes long. With the
information stored in each partition record, a GPT disk needs 16,384
bytes=32 sectors. Therefore, the first available sector is 34. Make
things “pristine,” as alluded to in the ubuntu document, you could start
the first partition at sector 40.
A GPT formatted disk can be told to set up for a different number of
partitions. What if you wanted (improbably) a capacity of 256
partitions. Then 32 sectors is not enough.
I’ve discovered also that gdisk by default is aligned to
"2048-sector boundaries,” and I agree that’s a good convention. Some people
might
call that “wasted space,” but it’s available to use for whatever reason.
Files are allocated in 4K blocks on ext partitions. On average, that's
2K per file. After 500 files, you've "wasted" that same 1M. Keep it in
perspective. On a small 60G drive, 1M is 0.0016% of the drive.
The 100M thing is probably true. I *think* it’s convention rather
thanstandard. It needs be only large enough to hold a grub, in this case, image.
GRUB on a BIOS system fits in 31.5K (track 1). 1 MiB is way more than
it needs, but keeping all partitions on 1 MiB boundaries just makes
sense. 100 MB is confusing the /boot partition with the grub partition.
-- Bruce
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