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Chapter 2. Planning 11

2.3 Disk planning

There are different aspects to consider when planning how to choose and allocate disk

storage. Some aspects include the following items:

򐂰 Conventional ECKD DASD versus FBA disks over SCSI/FCP

򐂰 3390-3s versus 3390-9s or large disk support

򐂰 Amount of disk storage per Linux image and how to allocate file systems

DASD versus SCSI/FCP

This book describes how to use conventional ECKD DASDs and does not discuss FBA disks

accessed over SCSI/FCP, not because either technology is superior, but simply because

DASDs seems to be much more common than SCSI/FCP disks. If you were to use SCSI/FCP

disks, cloning with the clone.sh script would have to be modified to account for World Wide

Port Names and Numbers. Sometimes a combination of these two types of disk storage is

used; when that is the case, the ECKD emulated DASD is often used for the root file system

and SCSI/FCP disks are used for large data storage areas.

3390-3s versus 3390-9s

Emulated 3390-3s format to about 2.3 GB, while 3390-9s are three times the size of emulated

3390-3s, or about 6.8 GB. Either size will work, although 3390-3s have been recommended

over 3390-9s by some performance analysts. This book describes mainly using 3390-3s,

however, and comments are added where using 3390-9s differs, especially with installing

z/VM.

Disk storage per Linux image

Disk storage has the following characteristics:

򐂰 You should use two 3390-3 DASD to create minidisks at virtual addresses 100 and 101,

instead of a single minidisk at virtual address 100.

򐂰 The root file system is on /dev/dasda1 with a recommended size of 384 MB. It is not a

logical volume, so if there are any problems with LVM, the system will still be able to boot.

򐂰 Other file systems are on logical volumes that are part of single volume group have the

characteristics shown in Table 2-1.

Table 2-1 Recommended logical volume file systems and sizes

This layout uses about 3.5 GB of 4.5 GB of disk space. You could choose to use other disk

sizes than 3338 cylinders (3390-3 minus cylinder 0). For example, if you chose to use

3390-9s, you could give addresses 100 and 101 each half of the volume, giving each Linux

about 6.8 GB of disk space.

Mount point Logical volume name Size

/usr/ usr-lv 2 GB

/var/ var-lv 512 MB

/opt/ opt-lv 384 MB

/tmp/ tmp-lv 384 MB

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 295 296

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Red Hat LINUX VIRTUAL SERVER 4.6 - ADMINISTRATION Manuale di Installazione Pagina 31