Handbook:SPARC/Blocks/Disks/en
Partition tables
Although it is theoretically possible to use a raw, unpartitioned disk to house a Linux system (when creating a btrfs RAID for example), this is almost never done in practice. Instead, disk block devices are split up into smaller, more manageable block devices. On sparc systems, these are called partitions. There are currently two standard partitioning technologies in use: Sun and GPT; the latter is supported only on more recent systems with a sufficiently recent firmware.
GUID Partition Table (GPT)
The GUID Partition Table (GPT) setup (also called GPT disklabel) uses 64-bit identifiers for the partitions. The location in which it stores the partition information is much bigger than the 512 bytes of the MBR partition table (DOS disklabel), which means there is practically no limit on the amount of partitions for a GPT disk. Also the size of a partition is bounded by a much greater limit (almost 8 ZiB - yes, zebibytes).
GPT also takes advantage of checksumming and redundancy. It carries CRC32 checksums to detect errors in the header and partition tables and has a backup GPT at the end of the disk. This backup table can be used to recover damage of the primary GPT near the beginning of the disk.
GPT is only supported on Oracle SPARC machines of the T4 generation or newer. Additionally, only certain more recent firmware includes GPT support. There are several methods to check whether GPT support is available.
From the OBP prompt, execute:
{0} okcd /packages/disk-label{0} ok.propertiessupported-labels gpt
sun
mbr
name disk-labelIf gpt is included in the output, then GPT support is available. Alternatively, this can be determined from the installation media without entering OBP. Use the prtconf command from sys-apps/sparc-utils to access this information from userspace:
root #prtconf -pv | grep -c gptOr, check if the file /sys/firmware/devicetree/base/packages/disk-label/gpt exists. If none of these methods succeeds, then a firmware update is required in order to support GPT.
Sun partition table
Systems not manufactured by Oracle, T3 or earlier systems, or systems running an earlier firmware must use the Sun partition table type.
The third partition on Sun systems is set aside as a special "whole disk" slice. This partition must not contain a file system.
Users who are used to the DOS partitioning scheme should note that Sun partition tables do not have "primary" and "extended" partitions. Instead, up to eight partitions are available per drive, with the third of these being reserved.
The Handbook authors suggest using GPT whenever possible for Gentoo installations.
Default partitioning scheme
Due to the differences in required partition layout between GPT and Sun partition tables, a single partitioning scheme is not sufficient to support all possible system requirements. Some example schemes are provided below.
GPT partition scheme
The following partitioning scheme will be used as an example for GPT-formatted disks:
| Partition | Filesystem | Size | Mount Point | Description |
|---|---|---|---|---|
| /dev/sda1 | (none) | 2M | none | BIOS boot partition |
| /dev/sda2 | (swap) | RAM size * 2 | none | Swap partition |
| /dev/sda3 | ext4 | Rest of the disk | / | Root partition |
Sun formatted partition scheme
The following partitioning scheme will be used as an example for Sun-formatted disks:
| Partition | Filesystem | Size | Mount Point | Description |
|---|---|---|---|---|
| /dev/sda1 | ext4 | Disk size minus swap | / | Root partition |
| /dev/sda2 | (swap) | RAM size * 2 | none | Swap partition |
| /dev/sda3 | (none) | Whole disk | none | Whole disk partition.
Required on disks using the Sun partition table. |
SPARC systems using OBP version 3 or older have additional restrictions on their partitioning scheme. The root partition must be the first partition on the disk, and it may be no larger than 2 GiB. For this reason, such systems will require additional sufficiently-sized partitions for top-level directories, such as /usr, /var, /home, and other directories which would likely cause the root partition to exceed this limit. These systems are also likely to require the Sun partition table type, so do not forget to include the whole disk partition.
Partitioning the disk with GPT
The following parts explain how to create the example partition layout for a GPT installation using fdisk. The example partition layout was mentioned earlier:
| Partition | Description |
|---|---|
| /dev/sda1 | Boot partition |
| /dev/sda2 | Swap partition |
| /dev/sda3 | Root partition |
Change the partition layout according the system's needs.
Viewing the current partition layout
fdisk is a popular and powerful tool to split a disk into partitions. Fire up fdisk against the disk (in the example, /dev/sda is used):
root #fdisk /dev/sdaUse the p key to display the disk's current partition configuration:
Command (m for help):pDisk /dev/sda: 14.57 GiB, 15640625152 bytes, 30548096 sectors Disk model: USB Flash Disk Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: 9850A2C2-76C4-FC47-9F0B-DA60449D2413 Device Start End Sectors Size Type /dev/sda1 2048 30547967 30545920 14.6G Linux filesystem
Creating a new disklabel and removing all existing partitions
Type g to create a new GPT disklabel on the disk; this will remove all existing partitions.
Command (m for help):gCreated a new GPT disklabel (GUID: 9850A2C2-76C4-FC47-9F0B-DA60449D2413).
For an existing GPT disklabel (see the output of p above), alternatively consider removing the existing partitions one by one from the disk. Type d to delete a partition. For instance, to delete an existing /dev/sda1:
Command (m for help):dSelected partition 1 Partition 1 has been deleted.
The partition has now been scheduled for deletion. It will no longer show up when printing the list of partitions (p, but it will not be erased until the changes have been saved. This allows users to abort the operation if a mistake was made - in that case, type q immediately and hit Enter and the partition will not be deleted.
Repeatedly type p to print out a partition listing and then type d and the number of the partition to delete it. Eventually, the partition table will be empty:
Command (m for help):pDisk /dev/sda: 14.57 GiB, 15640625152 bytes, 30548096 sectors Disk model: USB Flash Disk Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: 9850A2C2-76C4-FC47-9F0B-DA60449D2413
Now that the in-memory partition table is empty, we're ready to create the partitions.
Creating the BIOS boot partition
First, create the BIOS boot partition. Type n to create a new partition, followed by 1 to select the first partition. When prompted for the first sector, make sure it starts from 2048 (which may be needed for the boot loader) and hit Enter. When prompted for the last sector, type +2M to create a partition 2 Mbyte in size:
Command (m for help):nPartition number (1-128, default 1):
First sector (2048-30548062, default 2048):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-30548062, default 30547967): +2M
Created a new partition 1 of type 'Linux filesystem' and of size 2 MiB.
Mark the partition as a BIOS boot partition:
Command (m for help):tSelected partition 1 Partition type or alias (type L to list all): 4 Changed type of partition 'Linux filesystem' to 'BIOS boot'.
Creating the swap partition
Next, to create the swap partition, type n to create a new partition, then type 2 to create the second partition, /dev/sda2. When prompted for the first sector, hit Enter. When prompted for the last sector, type +4G (or any other size needed for the swap space) to create a partition 4 GiB in size.
Command (m for help):nPartition number (2-128, default 2):
First sector (6144-30548062, default 6144):
Last sector, +/-sectors or +/-size{K,M,G,T,P} (6144-30548062, default 30547967): +4G
Created a new partition 2 of type 'Linux filesystem' and of size 4 GiB.
After all this is done, type t to set the partition type, 2 to select the partition just created and then type in 19 to set the partition type to "Linux Swap".
Command (m for help):tPartition number (1,2, default 2): 2 Partition type (type L to list all types): 19 Changed type of partition 'Linux filesystem' to 'Linux swap'.
Creating the root partition
Finally, to create the root partition, type n to create a new partition. Then type 3 to create the third partition, /dev/sda3. When prompted for the first sector, hit Enter. When prompted for the last sector, hit Enter to create a partition that takes up the rest of the remaining space on the disk. After completing these steps, typing p should display a partition table that looks similar to this:
Command (m for help):pDisk /dev/sda: 14.57 GiB, 15640625152 bytes, 30548096 sectors Disk model: USB Flash Disk Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: 9850A2C2-76C4-FC47-9F0B-DA60449D2413 Device Start End Sectors Size Type /dev/sda1 2048 6143 4096 2M BIOS boot /dev/sda2 6144 8394751 8388608 4G Linux swap /dev/sda3 8394752 30547967 22153216 10.6G Linux filesystem
Saving the partition layout
To save the partition layout and exit fdisk, type w.
Command (m for help):wWith the partitions created, it is now time to put filesystems on them.
Partitioning the disk with a Sun partition table
The following parts explain how to create the example partition layout for a Sun partition table installation using fdisk. The example partition layout was mentioned earlier:
| Partition | Description |
|---|---|
| /dev/sda1 | Root partition |
| /dev/sda2 | Swap partition |
| /dev/sda3 | Whole disk partition |
Change the partition layout according to personal preference. If partitioning for a system using OBP version 3 or earlier, ensure that the root partition is less than 2G in size, and additionally create partitions /dev/sda4 and onward for additional filesystems.
Viewing the current partition layout
fdisk is a popular and powerful tool to split a disk into partitions. Fire up fdisk against the disk (in our example, we use /dev/sda):
root #fdisk /dev/sdaUse the p key to display the disk's current partition configuration:
Command (m for help):pDisk model: USB Flash Disk Geometry: 64 heads, 32 sectors/track, 14916 cylinders Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: sun Device Start End Sectors Size Id Type Flags /dev/sda1 0 30445567 30445568 14.5G 83 Linux native /dev/sda2 30445568 30547967 102400 50M 82 Linux swap u /dev/sda3 0 30547967 30547968 14.6G 5 Whole disk
Creating a new disklabel / removing all partitions
Type s to create a new Sun disklabel on the disk; this will remove all existing partitions.
Command (m for help):sCreated a new partition 1 of type 'Linux native' and of size 14.5 GiB. Created a new partition 2 of type 'Linux swap' and of size 50 MiB. Created a new partition 3 of type 'Whole disk' and of size 14.6 GiB. Created a new Sun disklabel.
For an existing Sun disklabel (see the output of p above), alternatively consider removing the existing partitions one by one from the disk. Type d to delete a partition. For instance, to delete an existing /dev/sda1:
Command (m for help):dPartition number (1-3, default 3): 1 Partition 1 has been deleted.
The partition has now been scheduled for deletion. It will no longer show up when printing the list of partitions (p, but it will not be erased until the changes have been saved. This allows users to abort the operation if a mistake was made - in that case, type q immediately and hit Enter and the partition will not be deleted.
Repeatedly type p to print out a partition listing and then type d and the number of the partition to delete it. Eventually, the partition table will be empty:
Command (m for help):pDisk /dev/sda: 14.57 GiB, 15640625152 bytes, 30548096 sectors Disk model: USB Flash Disk Geometry: 64 heads, 32 sectors/track, 14916 cylinders Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: sun
Now that the in-memory partition table is empty, we're ready to create the partitions.
Creating the whole disk partition
First, create the whole disk partition. Type n to create a new partition, followed by 3 to select the third partition. When prompted for the first sector, hit Enter. When prompted for the last sector, hit Enter to create a partition that takes up all of the space on the disk.
Command (m for help):nPartition number (1-8, default 1): 3
It is highly recommended that the third partition covers the whole disk and is of type `Whole disk'
First sector (0-30547968, default 0):
Last sector or +/-sectors or +/-size{K,M,G,T,P} (0-30547968, default 30547968):
Created a new partition 3 of type 'Whole disk' and of size 14.6 GiB.
fdisk will automatically set the type of such a partition to 'Whole disk', so there is no need to explicitly set the type.
Creating the root partition
Next, to create the root partition, type n to create a new partition. Then type 1 to create the third partition, /dev/sda1. When prompted for the first sector, hit Enter. When prompted for the last sector, type -4G (or whatever space is required for non-root partitions). After completing these steps, typing p should display a partition table that looks similar to this:
Command (m for help):pDisk /dev/sda: 14.57 GiB, 15640625152 bytes, 30548096 sectors Disk model: USB Flash Disk Geometry: 64 heads, 32 sectors/track, 14916 cylinders Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: sun Device Start End Sectors Size Id Type Flags /dev/sda1 0 22159359 22159360 10.6G 83 Linux native /dev/sda3 0 30547967 30547968 14.6G 5 Whole disk
Creating the swap partition
Finally, to create the swap partition, type n to create a new partition, then type 2 to create the second partition, /dev/sda2. When prompted for the first sector, hit Enter. When prompted for the last sector, hit Enter to take up the remaining space on the disk.
Command (m for help):nPartition number (2,4-8, default 2):
First sector (22159360-30547968, default 22159360):
Last sector or +/-sectors or +/-size{K,M,G,T,P} (22159360-30547968, default 30547968):
Created a new partition 2 of type 'Linux native' and of size 4 GiB.
After all this is done, type t to set the partition type, 2 to select the partition just created and then type in 82 to set the partition type to "Linux Swap".
Command (m for help):tPartition number (1-3, default 3): 2 Hex code (type L to list all codes): 82 Changed type of partition 'Linux native' to 'Linux swap'.
After completing these steps, typing p should display a partition table that looks similar to this:
Command (m for help):pDisk /dev/sda: 14.57 GiB, 15640625152 bytes, 30548096 sectors Disk model: USB Flash Disk Geometry: 64 heads, 32 sectors/track, 14916 cylinders Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: sun Device Start End Sectors Size Id Type Flags /dev/sda1 0 22159359 22159360 10.6G 83 Linux native /dev/sda2 22159360 30547967 8388608 4G 82 Linux swap u /dev/sda3 0 30547967 30547968 14.6G 5 Whole disk
Saving the partition layout
To save the partition layout and exit fdisk, type w.
Command (m for help):wWith the partitions created, it is now time to put filesystems on them.