Installer causes sector misalignment with Advanced Format hard drive
| Project: | Trisquel |
| Component: | Installer |
| Category: | bug report |
| Priority: | normal |
| Assigned: | Unassigned |
| Status: | active |
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Hardware used
Laptop: Thinkpad T61
Hard Drive: Western Digital Scorpio Black 500GB 2.5" (WD5000BPKT)
This hard drive uses Advanced Format and requires partitions to be aligned on specific sector multiples for optimal performance.
Intended action
During Installer's Manual partitioning step, do a manual partitioning with 1 Primary partition and 1 Extended partition with at least 4 Logical Partitions.
Result
After installation, Disk Utility displays "Warning: The partition is misaligned by XXX bytes. This may result in very poor performance. Repartitioning is suggested." when clicking on the Extended partition. The Primary partition and the Logical partitions did not show this warning.
Alternative attempts
Various different partitioning schemes were attempted with GParted prior to running the installer. During the Installer's Manual partitioning step the previously created partitions were marked to be formatted and matched to the various mount points. No size changes were made.
Attempt 1
The same original layout was made using the following settings:
* 1 MiB preceding each Primary/Logical partition.
* Align To: MiB
* Extended partition did not have 1 MiB preceding.
After partitioning, the sectors were properly aligned according to fdisk:
~# fdisk -u -l /dev/sda Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x000e1da5 Device Boot Start End Blocks Id System /dev/sda1 2048 206847 102400 83 Linux /dev/sda2 206848 976773119 488283136 5 Extended /dev/sda5 208896 105066495 52428800 83 Linux /dev/sda6 105068544 121845759 8388608 82 Linux swap / Solaris /dev/sda7 121847808 792936447 335544320 83 Linux /dev/sda8 792938496 876824575 41943040 83 Linux /dev/sda9 876826624 976773119 49973248 83 Linux
After installation:
~# fdisk -u -l /dev/sda Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x00017296 Device Boot Start End Blocks Id System /dev/sda1 * 2048 206847 102400 83 Linux /dev/sda2 208894 976773119 488282113 5 Extended Partition 2 does not start on physical sector boundary. /dev/sda5 208896 105066495 52428800 83 Linux /dev/sda6 105068544 121845759 8388608 82 Linux swap / Solaris /dev/sda7 121847808 792936447 335544320 83 Linux /dev/sda8 792938496 876824575 41943040 83 Linux /dev/sda9 876826624 976773119 49973248 83 Linux
Attempt 2
The same process as Attempt 1, but this time 1 MiB preceding was used when adding the extended partition.
Again, it was properly aligned after partitioning:
~# fdisk -l -u /dev/sda Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x000e1da5 Device Boot Start End Blocks Id System /dev/sda1 2048 206847 102400 83 Linux /dev/sda2 208896 976773119 488282112 5 Extended /dev/sda5 210944 105066495 52427776 83 Linux /dev/sda6 105068544 121845759 8388608 82 Linux swap / Solaris /dev/sda7 121847808 792936447 335544320 83 Linux /dev/sda8 792938496 876824575 41943040 83 Linux /dev/sda9 876826624 976773119 49973248 83 Linux
After installation:
~# fdisk -l -u /dev/sda Disk /dev/sda: 500.1 GB, 500107862016 bytes 255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk identifier: 0x000e1da5 Device Boot Start End Blocks Id System /dev/sda1 * 2048 206847 102400 83 Linux /dev/sda2 210942 976773119 488281089 5 Extended Partition 2 does not start on physical sector boundary. /dev/sda5 210944 105066495 52427776 83 Linux /dev/sda6 105068544 121845759 8388608 82 Linux swap / Solaris /dev/sda7 121847808 792936447 335544320 83 Linux /dev/sda8 792938496 876824575 41943040 83 Linux /dev/sda9 876826624 976773119 49973248 83 Linux
Notes
I did not test with the default install option (Use entire disk).
Possible workarounds
Workaround 1: Use only Primary partitions
Using GParted, create only Physical partitions with the following settings:
* 1 MiB preceding
* Aligned to MiB
The default boot record uses MBR and allows only 4 primary partitions.
Workaround 2: GUID Partition Table (GPT)
If you need more than 4 partitions, use GParted to create a new GPT partition table. This might possibly not be supported by older hardware.
You will need to add a small (<=4MiB) partition at the front for the BIOS boot information. Thereafter you can add Physical partitions.
All these partitions should use the same settings as above.
In addition, the small BIOS boot partition needs to have the "bios_grub" flag set. Without this partition GRUB will not install.
Thereafter you can run the installer and select the appropriate mount points. Do not assign anything to the small BIOS boot partition.
Note that in both of these workarounds you will end up with 1 MiB-sized partitions between all your actual partitions. You can ignore those.
After installation your partitions should still be correctly aligned.