Why 262144 blocks next to each partition?
Why 262144 blocks next to each partition?
- Subject: Why 262144 blocks next to each partition?
- From: Howard Gayle <email@hidden>
- Date: Tue, 01 Aug 2006 13:11:39 -0400
On 10.4.7, diskutil (or Disk Utility) places an area of 262144
512-byte blocks after each GPT partition, except the last
partition, which gets 262151 512-byte blocks.
Here's an example of partitioning a 320 GB disk into 7
partitions:
diskutil partitionDisk disk1 7 GPTFormat \
'Journaled HFS+' s01b_root0 53.9G \
UFS s01b_utils0 43.2G \
'Journaled HFS+' s01b_root1 53.9G \
UFS s01b_utils1 43.2G \
'Journaled HFS+' s01b_root2 53.9G \
UFS s01b_utils2 43.2G \
'Journaled HFS+' s01b_rest 1G
Finished partitioning on disk disk1
/dev/disk1
#: type name size identifier
0: GUID_partition_scheme *298.1 GB disk1
1: EFI 200.0 MB disk1s1
2: Apple_HFS s01b_root0 53.8 GB disk1s2
3: Apple_UFS s01b_utils0 41.7 GB disk1s3
4: Apple_HFS s01b_root1 53.8 GB disk1s4
5: Apple_UFS s01b_utils1 41.7 GB disk1s5
6: Apple_HFS s01b_root2 53.8 GB disk1s6
7: Apple_UFS s01b_utils2 41.7 GB disk1s7
8: Apple_HFS s01b_rest 6.5 GB disk1s8
Now look what gpt(8) shows:
sudo gpt -r -v show /dev/disk1
gpt show: /dev/disk1: mediasize=320072933376; sectorsize=512; blocks=625142448
start size index contents
0 1 PMBR
1 1 Pri GPT header
2 32 Pri GPT table
34 6
40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
409640 112774352 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
113183992 262144
113446136 90334824 3 GPT part - 55465300-0000-11AA-AA11-00306543ECAC
203780960 262144
204043104 112774352 4 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
316817456 262144
317079600 90334824 5 GPT part - 55465300-0000-11AA-AA11-00306543ECAC
407414424 262144
407676568 112774352 6 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
520450920 262144
520713064 90334824 7 GPT part - 55465300-0000-11AA-AA11-00306543ECAC
611047888 262144
611310032 13570232 8 GPT part - 48465300-0000-11AA-AA11-00306543ECAC
624880264 262151
625142415 32 Sec GPT table
625142447 1 Sec GPT header
With an Apple partition map it looks like this:
diskutil partitionDisk disk1 7 APMFormat \
'Journaled HFS+' s01b_root0 53.9G \
UFS s01b_utils0 43.2G \
'Journaled HFS+' s01b_root1 53.9G \
UFS s01b_utils1 43.2G \
'Journaled HFS+' s01b_root2 53.9G \
UFS s01b_utils2 43.2G \
'Journaled HFS+' s01b_rest 1G
Finished partitioning on disk disk1
/dev/disk1
#: type name size identifier
0: Apple_partition_scheme *298.1 GB disk1
1: Apple_partition_map 31.5 KB disk1s1
2: Apple_HFS s01b_root0 53.8 GB disk1s3
3: Apple_Boot 8.5 MB disk1s4
4: Apple_UFS s01b_utils0 41.9 GB disk1s5
5: Apple_HFS s01b_root1 53.8 GB disk1s7
6: Apple_Boot 8.5 MB disk1s8
7: Apple_UFS s01b_utils1 41.9 GB disk1s9
8: Apple_HFS s01b_root2 53.8 GB disk1s11
9: Apple_Boot 8.5 MB disk1s12
10: Apple_UFS s01b_utils2 41.9 GB disk1s13
11: Apple_HFS s01b_rest 6.7 GB disk1s15
3:17
sudo pdisk
e /dev/rdisk1
p
Partition map (with 512 byte blocks) on '/dev/rdisk1'
#: type name length base ( size )
1: Apple_partition_map Apple 63 @ 1
2: Apple_Free 262144 @ 64 (128.0M)
3: Apple_HFS Apple_HFS_Untitled_1 112774352 @ 262208 ( 53.8G)
4: Apple_Boot eXternal booter 17408 @ 113036560 ( 8.5M)
5: Apple_UFS Apple_UFS_Untitled_2 90579560 @ 113053968 ( 43.2G)
6: Apple_Free 262144 @ 203633528 (128.0M)
7: Apple_HFS Apple_HFS_Untitled_3 112774352 @ 203895672 ( 53.8G)
8: Apple_Boot eXternal booter 17408 @ 316670024 ( 8.5M)
9: Apple_UFS Apple_UFS_Untitled_4 90579560 @ 316687432 ( 43.2G)
10: Apple_Free 262144 @ 407266992 (128.0M)
11: Apple_HFS Apple_HFS_Untitled_5 112774352 @ 407529136 ( 53.8G)
12: Apple_Boot eXternal booter 17408 @ 520303488 ( 8.5M)
13: Apple_UFS Apple_UFS_Untitled_6 90579560 @ 520320896 ( 43.2G)
14: Apple_Free 262144 @ 610900456 (128.0M)
15: Apple_HFS Apple_HFS_Untitled_7 13979832 @ 611162600 ( 6.7G)
16: Apple_Free 16 @ 625142432
Device block size=512, Number of Blocks=625142448 (298.1G)
This time, the 262144-block area comes before each partition, and
the one at the end is the same size.
I didn't notice anything in IOApplePartitionScheme or
IOGUIDPartitionScheme that seemed to be looking for these areas.
What are they for?
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