Re: Wasted space in hard disk partitioning (was Soliciting Hardware Recommendations)
On Tue, Dec 17, 2013 at 4:12 AM, Stephen Powell <zlinuxman@wowway.com> wrote:
> On Mon, 16 Dec 2013 08:13:16 -0600, Stan Hoeppner wrote:
>>
>> Cool. Make sure you partition the SSD so that your first, and all,
>> partitions start on a 4KB boundary. Many guides are available for your
>> favorite partitioning tool. Linux does all IO in 4KB pages including
>> filesystem and swap. If you don't align to 4KB you may get excessive
>> erase cycles on the SSD, lowering performance, and cell life. Most
>> folks seem to start the first SSD partition at sector 2048, which falls
>> immediately after the first 1MB of the device. 1,048,576/4,096=256. So
>> your first partition will start at 4KB "page 257", if you will. If you
>> create multiple partitions, make sure the size of each is evenly
>> divisible by 4096 bytes, or they won't be aligned.
>
> That's good to know. But I really don't have much control over this
> when I partition using the Debian installer. When installing from
> scratch on a system where I don't intend to keep anything from its
> previous life, I delete all existing partitions using the Debian installer,
> then create new partitions using the Debian installer. When I create
> a new partition with the Debian installer, I generally specify the size
> (typically in megabytes), the partition type (primary or logical), and,
> if the size is less than the amount of free space, whether I want it at
> the beginning of the free space or the end of the free space. Rounding
> of sizes, boundary alignment, etc. is all controlled by the Debian installer
> or the partitioning tools it uses (parted, generally). And I have no
> control over that.
>
> As an example, my existing disk partitions, created by the Debian installer,
> look like this:
>
> # parted /dev/i2o/hda unit s print free
> Model: I2O Controller (i2o)
> Disk /dev/i2o/hda: 286748672s
> Sector size (logical/physical): 512B/512B
> Partition table: msdos
>
> Number Start End Size Type File system Flags
> 63s 2047s 1985s Free Space
> 1 2048s 194559s 192512s primary ext3 boot
> 194560s 196605s 2046s Free Space
> 2 196606s 162306302s 162109697s extended
> 5 196608s 17772543s 17575936s logical linux-swap(v1)
> 6 17774592s 56834047s 39059456s logical ext3
> 7 56836096s 64647167s 7811072s logical ext3
> 8 64647231s 162306302s 97659072s logical ext3
> 162306303s 286748671s 124442369s Free Space
>
> #
>
> As you can see, something, somewhere, has done a number on me. The only
> boundary requirement is that the starting sector be a multiple of 8 to make
> 4096-byte boundaries. So why start the first partition at sector number
> 2048? The only intentional free space is the free space at the end of the
> disk. The other free space entries were added by the partitioning program.
> And for what purpose? This is not a GPT disk, so no BIOS boot partition
> needs to be created for GRUB. (I'm not even using GRUB, I'm using LILO.
> But the Debian installer would not have known what boot loader I planned
> to use during the disk partitioning phase. It would, however, have known
> that this is an MBR disk, not a GPT disk.) Furthermore, this is not a
> UEFI-based system, so no EFI System partition (ESP) needs to be created
> either. So why did the Debian installer leave these two free spaces before
> and after my first partition? (Apparently, sectors 0-62 are considered part
> of "meta data" and are therefore not included in the leading free space.)
>
> Also, as you can see, the start of the next partition is not just one sector
> number higher than the end of the previous partition. In the case of adjacent
> logical partitions inside the extended partition, I realize that it must
> leave room for an Extended Boot Record before each logical partition, but it
> leaves way more room than that would require. Can you (or anyone) explain
> why this wasted space has been built in?
Current practice is that all partitions should start at a multiple of
1 MiB in order for these partitions to be aligned with different types
of hardware.
Your data partitions #1,5,6,7 start on a multiple of 2048s, hence the
gaps between them and the gap before #1.
Somehow #7 and #8 only have a gap of 63s between them. Did you create
#8 via d-i or post-install?
Regarding the 0-62 sectors: the "specialness" of these sectors is
historical because sector 0 contained the MBR and the first partition
started at the second track - and there were 63 sectors per track.
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