Handbook:SPARC/Installation/Disks
Introduction to block devices
Block devices
Let's take a good look at disk-oriented aspects of Gentoo Linux and Linux in general, including block devices, partitions, and Linux filesystems. Once the ins and outs of disks are understood, partitions and filesystems can be established for installation.
To begin, let's look at block devices. SCSI and Serial ATA drives are both labeled under device handles such as: /dev/sda, /dev/sdb, /dev/sdc, etc. On more modern machines, PCI Express based NVMe solid state disks have device handles such as /dev/nvme0n1, /dev/nvme0n2, etc.
The following table will help readers determine where to find a certain type of block device on the system:
| Type of device | Default device handle | Editorial notes and considerations |
|---|---|---|
| SATA, SAS, SCSI, or USB flash | /dev/sda | Found on hardware from roughly 2007 until the present, this device handle is perhaps the most commonly used in Linux. These types of devices can be connected via the SATA bus, SCSI, USB bus as block storage. As example, the first partition on the first SATA device is called /dev/sda1. |
| NVM Express (NVMe) | /dev/nvme0n1 | The latest in solid state technology, NVMe drives are connected to the PCI Express bus and have the fastest transfer block speeds on the market. Systems from around 2014 and newer may have support for NVMe hardware. The first partition on the first NVMe device is called /dev/nvme0n1p1. |
| MMC, eMMC, and SD | /dev/mmcblk0 | embedded MMC devices, SD cards, and other types of memory cards can be useful for data storage. That said, many systems may not permit booting from these types of devices. It is suggested to not use these devices for active Linux installations; rather consider using them to transfer files, which is their design goal. Alternatively they could be useful for short-term backups. |
The block devices above represent an abstract interface to the disk. User programs can use these block devices to interact with the disk without worrying about whether the drives are SATA, SCSI, or something else. The program can simply address the storage on the disk as a bunch of contiguous, randomly-accessible 4096-byte (4K) blocks.
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 <!--T:79--> 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
<!--T:92-->
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
<!--T:98-->
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 <!--T:104--> 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 <!--T:117--> 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 <!--T:123--> 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
<!--T:131-->
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):
<!--T:132-->
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 <!--T:137--> 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 <!--T:138-->
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):
<!--T:142-->
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 <!--T:145--> 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 <!--T:148--> 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.
Creating file systems
Introduction
Now that the partitions have been created, it is time to place a filesystem on them. In the next section the various file systems that Linux supports are described. Readers that already know which filesystem to use can continue with Applying a filesystem to a partition. The others should read on to learn about the available filesystems...
Filesystems
Linux supports several dozen filesystems, although many of them are only wise to deploy for specific purposes. Only certain filesystems may be found stable on the sparc architecture - it is advised to read up on the filesystems and their support state before selecting a more experimental one for important partitions. ext4 is the recommended all-purpose, all-platform filesystem. The below is a non-exaustive list
- btrfs
- A next generation filesystem that provides many advanced features such as snapshotting, self-healing through checksums, transparent compression, subvolumes, and integrated RAID. Kernels prior to 5.4.y are not guaranteed to be safe to use with btrfs in production because fixes for serious issues are only present in the more recent releases of the LTS kernel branches. Filesystem corruption issues are common on older kernel branches, with anything older than 4.4.y being especially unsafe and prone to corruption. Corruption is more likely on older kernels (than 5.4.y) when compression is enabled. RAID 5/6 and quota groups unsafe on all versions of btrfs. Furthermore, btrfs can counter-intuitively fail filesystem operations with ENOSPC when df reports free space due to internal fragmentation (free space pinned by DATA + SYSTEM chunks, but needed in METADATA chunks). Additionally, a single 4K reference to a 128M extent inside btrfs can cause free space to be present, but unavailable for allocations. This can also cause btrfs to return ENOSPC when free space is reported by df. Installing sys-fs/btrfsmaintenance and configuring the scripts to run periodically can help to reduce the possibility of ENOSPC issues by rebalancing btrfs, but it will not eliminate the risk of ENOSPC when free space is present. Some workloads will never hit ENOSPC while others will. If the risk of ENOSPC in production is unacceptable, you should use something else. If using btrfs, be certain to avoid configurations known to have issues. With the exception of ENOSPC, information on the issues present in btrfs in the latest kernel branches is available at the btrfs status page.
- ext4
- Initially created as a fork of ext3, ext4 brings new features, performance improvements, and removal of size limits with moderate changes to the on-disk format. It can span volumes up to 1 EB and with maximum file size of 16TB. Instead of the classic ext2/3 bitmap block allocation, ext4 uses extents, which improve large file performance and reduce fragmentation. Ext4 also provides more sophisticated block allocation algorithms (delayed allocation and multiblock allocation) giving the filesystem driver more ways to optimize the layout of data on the disk. Ext4 is the recommended all-purpose all-platform filesystem.
- f2fs
- The Flash-Friendly File System was originally created by Samsung for the use with NAND flash memory. As of Q2, 2016, this filesystem is still considered immature, but it is a decent choice when installing Gentoo to microSD cards, USB drives, or other flash-based storage devices.
- JFS
- IBM's high-performance journaling filesystem. JFS is a light, fast, and reliable B+tree-based filesystem with good performance in various conditions.
- XFS
- A filesystem with metadata journaling which comes with a robust feature-set and is optimized for scalability. XFS seems to be less forgiving to various hardware problems, but has been continuously upgraded to include modern features.
- VFAT
- Also known as FAT32, is supported by Linux but does not support standard UNIX permission settings. It is mostly used for interoperability/interchange with other operating systems (Microsoft Windows or Apple's macOS) but is also a necessity for some system bootloader firmware (like UEFI). Users of UEFI systems will need an EFI System Partition formatted with VFAT in order to boot.
- NTFS
- This "New Technology" filesystem is the flagship filesystem of Microsoft Windows since Windows NT 3.1. Similarly to VFAT, it does not store UNIX permission settings or extended attributes necessary for BSD or Linux to function properly, therefore it should not be used as a filesystem for most cases. It should only be used for interoperability/interchange with Microsoft Windows systems (note the emphasis on only).
Applying a filesystem to a partition
To create a filesystem on a partition or volume, there are user space utilities available for each possible filesystem. Click the filesystem's name in the table below for additional information on each filesystem:
| Filesystem | Creation command | On minimal CD? | Package |
|---|---|---|---|
| btrfs | mkfs.btrfs | Yes | sys-fs/btrfs-progs |
| ext4 | mkfs.ext4 | Yes | sys-fs/e2fsprogs |
| f2fs | mkfs.f2fs | Yes | sys-fs/f2fs-tools |
| jfs | mkfs.jfs | Yes | sys-fs/jfsutils |
| reiserfs (deprecated) | mkfs.reiserfs | Yes | sys-fs/reiserfsprogs |
| xfs | mkfs.xfs | Yes | sys-fs/xfsprogs |
| vfat | mkfs.vfat | Yes | sys-fs/dosfstools |
| NTFS | mkfs.ntfs | Yes | sys-fs/ntfs3g |
For instance, to have the root partition (/dev/sda1) as ext4 as used in the example partition structure, the following commands would be used:
root #mkfs.ext4 /dev/sda1When using ext4 on a small partition (less than 8 GiB), then the file system must be created with the proper options to reserve enough inodes. This can be done using one of the following commands, respectively:
root #mkfs.ext4 -T small /dev/<device>This will generally quadruple the number of inodes for a given file system as its "bytes-per-inode" reduces from one every 16kB to one every 4kB.
Now create the filesystems on the newly created partitions (or logical volumes).
Activating the swap partition
mkswap is the command that is used to initialize swap partitions:
root #mkswap /dev/sda2To activate the swap partition, use swapon:
root #swapon /dev/sda2Create and activate the swap with the commands mentioned above.
Mounting the root partition
Users of non-Gentoo installation media will need to create the mount point by running:
root #mkdir --parents /mnt/gentooNow that the partitions have been initialized and are housing a filesystem, it is time to mount those partitions. Use the mount command, but don't forget to create the necessary mount directories for every partition created. As an example we mount the root partition:
root #mount /dev/sda1 /mnt/gentooIf /tmp/ needs to reside on a separate partition, be sure to change its permissions after mounting:
root #chmod 1777 /mnt/gentoo/tmpLater in the instructions the proc filesystem (a virtual interface with the kernel) as well as other kernel pseudo-filesystems will be mounted. But first we install the Gentoo installation files.