The possible origin of hd4 as / on AIX PDF Print E-mail
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Written by Michael Felt   
I had the pleasure of working on AIX 1 and AIX 2, but was never responsible for system management - at least not enough that I had cause to remember the names of the disk partitions - what AIX called minidisks in those days. In a now ancient FAQ (for AIX V2) I found what might "explain" how hd4 became / and hd1 became /home.

The question was - how to enlarge a filesystem - and as jfs was not a part of AIX V2, the answer was similiar as for any UNIX in those days - repartition the harddisk. From an excerpt I saw a list of the minidisk names, and all of a sudden I saw a possible explanation for the surprising partition names for root and home file systems.

     Procedure B - IF there is NOT ENOUGH free space:
4)  Select Backup commands.
5)  Select Backup a file system and backup the /usr filesystem.
a)  Repeat this step for the other filesystems that are on the
hard disk and physically located "behind" the /usr minidisk.
For example if a system only has one hard disk (70 Meg), the
minidisk facility gives the following information:
MD    MD     MD    Block Number ... Mount     ......
Name  IODN  Type  Size   Blocks ... Directory ......
hd6   32760 VRM   512    3600       /vrm
32766 Pgsp  512    13722
hd0   16384 AIX   512    25679      /
hd2   16387 AIX   512    66809      /usr
hd1   16386 AIX   512    22810      /u
hd3   16388 AIX   512    4000       /tmp
hd4   16385 AIX   512    5000              (the dump minidisk)
Available space   512    1000  
Assuming that there is some free space after hd4, then
backup the /usr and /u filesystems. You probably would not
backup the /tmp minidisk since you do not have any permanent
files there. You would not backup the dump minidisk (IODN

Do you see it? In AIX V2, root is hd0, /u (now /home) is hd1, hd2 and hd3 are the same as today, hd4 was dump - which became root (/). I don't see hd5 so I'll guess it was boot already, hd6 was paging, hd7 became the dump device in AIX V3 (in AIX 4 hd7 disappeared - hd6 functioned as dump on a crash - saving diskspace (in those days 64M Byte could be 10% or more of a disk) and hd8 - again AIX V3 becomes the jfslog. The new filesystems (/var and /opt) got pretty logical partition names hd9var and hd10opt. I wonder what hd11 will bring us?

And in case you want to see some history follow this link:
FAQ: AIX V2.2.1 on IBM RT systems



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