ハンドブック:IA64/ブロック/ディスク

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This page is a translated version of the page Handbook:IA64/Blocks/Disks and the translation is 31% complete.


パーティション

Although it is theoretically possible to use a full disk to house your Linux system, this is almost never done in practice. Instead, full disk block devices are split up in smaller, more manageable block devices. On IA64 systems, these are called partitions.

Itanium systems use EFI, the Extensible Firmware Interface, for booting. The partition table format that EFI understands is called GPT, or GUID Partition Table. The partitioning program that understands GPT is called "parted", so that is the tool used below. Additionally, EFI can only read FAT filesystems, so that is the format to use for the EFI boot partition, where the kernel will be installed by "elilo".

Advanced storage

The IA64 Installation CDs provide support for LVM2. LVM2 increases the flexibility offered by the partitioning setup. During the installation instructions, we will focus on "regular" partitions, but it is still good to know LVM2 is supported as well.

Designing a partition scheme

How many partitions and how big?

The number of partitions is highly dependent on the environment. For instance, if there are lots of users, then it is advised to have /home/ separate as it increases security and makes backups easier. If Gentoo is being installed to perform as a mail server, then /var/ should be separate as all mails are stored inside /var/. A good choice of filesystem will then maximize the performance. Game servers will have a separate /opt/ as most gaming servers are installed there. The reason is similar for the /home/ directory: security and backups. In most situations, /usr/ is to be kept big: not only will it contain the majority of applications, it typically also hosts the Gentoo ebuild repository (by default located at /var/db/repos/gentoo) which already takes around 650 MiB. This disk space estimate excludes the binpkgs/ and distfiles/ directories that are stored under /var/cache/ by default.

It very much depends on what the administrator wants to achieve. Separate partitions or volumes have the following advantages:

  • Choose the best performing filesystem for each partition or volume.
  • The entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume.
  • If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is more with multiple disks than it is with multiple partitions).
  • Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored), etc.

However, multiple partitions have disadvantages as well. If not configured properly, the system might have lots of free space on one partition and none on another. Another nuisance is that separate partitions - especially for important mount points like /usr/ or /var/ - often require the administrator to boot with an initramfs to mount the partition before other boot scripts start. This isn't always the case though, so results may vary.

There is also a 15-partition limit for SCSI and SATA unless the disk uses GPT labels.

What about swap space?

There is no perfect value for the swap partition. The purpose of swap space is to provide disk storage to the kernel when internal memory (RAM) is under pressure. A swap space allows for the kernel to move memory pages that are not likely to be accessed soon to disk (swap or page-out), freeing memory. Of course, if that memory is suddenly needed, these pages need to be put back in memory (page-in) which will take a while (as disks are very slow compared to internal memory).

When the system is not going to run memory intensive applications or the system has lots of memory available, then it probably does not need much swap space. However, swap space is also used to store the entire memory in case of hibernation. If the system is going to need hibernation, then a bigger swap space is necessary, often at least the amount of memory installed in the system.


Non-default example partition scheme

An example partitioning for a 20GB disk is shown below, used as a demonstration laptop (containing webserver, mailserver, gnome, ...):

root #df -h
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/sda5     ext4    509M  132M  351M  28% /
/dev/sda2     ext4    5.0G  3.0G  1.8G  63% /home
/dev/sda7     ext4    7.9G  6.2G  1.3G  83% /usr
/dev/sda8     ext4   1011M  483M  477M  51% /opt
/dev/sda9     ext4    2.0G  607M  1.3G  32% /var
/dev/sda1     ext2     51M   17M   31M  36% /boot
/dev/sda6     swap    516M   12M  504M   2% <not mounted>
(Unpartitioned space for future usage: 2 GB)

/usr/ is rather full (83% used) here, but once all software is installed, /usr/ doesn't tend to grow that much. Although allocating a few gigabytes of disk space for /var/ may seem excessive, remember that portage uses this partition by default for compiling packages. To keep /var/ at a more reasonable size, such as 1GB, alter the PORTAGE_TMPDIR variable in /etc/portage/make.conf to point to the partition with enough free space for compiling extremely large packages such as LibreOffice.

Using parted to partition the disk

The following parts explain how to create the example partition layout used in the remainder of the installation instructions, namely:

Partition Description
/dev/sda1 EFI Boot partition
/dev/sda2 Swap partition
/dev/sda3 Root partition

Change the partition layout according to personal preference.

Viewing the current partition layout

parted is the GNU partition editor. Fire up parted on the disk (in our example, we use /dev/sda):

root #parted /dev/sda

Once in parted, a prompt that looks like this shows up:

(parted)

At this point one of the available commands is help, to see the other available commands. Another command is print to display the disk's current partition configuration:

(parted)print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017    203.938  fat32                             boot
2        203.938   4243.468  linux-swap
3       4243.469  34724.281  ext4

This particular configuration is very similar to the one recommended above. Note on the second line that the partition table is type is GPT. If it is different, then the ia64 system will not be able to boot from this disk. To explain how partitions are created, let's first remove the partitions and recreate them.

Removing all partitions

Note
Unlike fdisk and some other partitioning programs which postpone committing changes until the write instruction is given, parted commands take effect immediately. So once partitions are added or removed, there is no undo.

The easy way to remove all partitions and start fresh, which guarantees that we are using the correct partition type, is to make a new partition table using the mklabel command. This results in an empty GPT partition table.

(parted) mklabelgpt
(parted) mklabelprint
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags

Now that the partition table is empty, we're ready to create the partitions. We will use a default partitioning scheme as discussed previously. Of course, don't follow these instructions to the letter but adjust to personal preference.

Creating the EFI boot partition

First create a small EFI boot partition. This is required to be a FAT filesystem in order for the IA64 firmware to read it. Our example makes this 32 MB, which is appropriate for storing kernels and elilo configuration. Expect each IA64 kernel to be around 5 MB, so this configuration leaves some room to grow and experiment.

(parted)mkpart primary fat32 0 32
(parted)print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017     32.000  fat32

Creating the swap partition

Let's now create the swap partition. The classic size to make the swap partition was twice the amount of RAM in the system. In modern systems with lots of RAM, this is no longer necessary. For most desktop systems, a 512 megabyte swap partition is sufficient. For a server, consider something larger to reflect the anticipated needs of the server.

(parted)mkpart primary linux-swap 32 544
(parted)print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017     32.000  fat32
2         32.000    544.000

Creating the root partition

Finally, create the root partition. Our configuration will make the root partition to occupy the rest of the disk. We default to ext4, but it is possible to use ext2, jfs, reiserfs or xfs. The actual filesystem is not created in this step, but the partition table contains an indication of what kind of filesystem is stored on each partition, and it's a good idea to make the table match the intentions.

(parted)mkpart primary ext4 544 34732.890
(parted)print
Disk geometry for /dev/sda: 0.000-34732.890 megabytes
Disk label type: gpt
Minor    Start       End     Filesystem  Name                  Flags
1          0.017     32.000  fat32
2         32.000    544.000
3        544.000  34732.874

Exiting parted

To quit from parted, type quit. There's no need to take a separate step to save the partition layout since parted has been saving it all along. Parted will give a reminder to update the /etc/fstab file, which is done later in the installation instructions.

(parted)quit
Information: Don't forget to update /etc/fstab, if necessary.