Handbook:SPARC/Blocks/Disks/ja

From Gentoo Wiki
Jump to:navigation Jump to:search
This page is a translated version of the page Handbook:SPARC/Blocks/Disks and the translation is 2% complete.


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.properties
gpt

supported-labels gpt

                   sun
                   mbr
name disk-label

If 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 gpt

Or, 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.

Important
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/sda

Use the p key to display the disk's current partition configuration:

Command (m for help):p
Disk /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):g
Created 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):d
Selected 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):p
Disk /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):n
Partition 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):t
Selected 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):n
Partition 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):t
Partition 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):p
Disk /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):w

With 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/sda

Use the p key to display the disk's current partition configuration:

Command (m for help):p
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 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):s
Created 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):d
Partition 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):p
Disk /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):n
Partition 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):p
Disk /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):n
Partition 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):t
Partition 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):p
Disk /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):w

With the partitions created, it is now time to put filesystems on them.