SUMMARY: increasing swap partition on 2.5.1

Date: Fri Oct 31 1997 - 06:27:44 CST

My original question, interleaved with a summary of responses :


>> I need to increase the active swap partition /dev/rdsk/c0t3d0s1 (2.5.1
>> boot disk) as I have undersized it during install.
>> I do not have any spare space on any other volumes, so I can't easily
>> add another swap file.
>> Looking at the partition information on c0t3d0 I have decided to
>> decrease the size of c0t3d0s3 (the next contiguous partition, used for
>> /export/home) and add the extra cylinders to s1 for swap.
>> This is what I thought I'd do, but not entirely sure if this is correct
>> (which is where you guys come in !) :

>> back up /export/home and take server (SS20 192Mb RAM) to single user
>> mode.
>> (perhaps) issue swap -d /dev/dsk/c0t3d0s1 to delete the swap space.
>> Reformatted the disk, increasing slice 1 accordingly and adjusting
>> beginning of slice 3 etc.
>> newfs c0t3d0s3 for /export/home.

The general concensus was that the above was fundamentally correct...

>> Do I need to do anything with c0t3d0s1 if i've left /etc/vfstab
>> intact ? Will swap automatically get adjusted after I reboot ?

Yes, swap will get adjusted if you leave /etc/vfstab as it is.

>> Also, IF i did get an extra disk, could I create a partition on it for
>> swap and just add a swap type entry in /etc/vfstab for that partition?

Yes, this is also perferable to a single swap partition. The OS will
interleave swap disk accesses across multiple partitions.

>> Where does the mkfile command fit into all this ?

This is what caused my confusion in the first place....the old swap
partition vs swap file chestnut.....
Here's what David Thorburn-Gundlach <> says......
"Aha! This explains all of the above :-) mkfile makes a file (clever, I
know) of a specified size, typically for use as an additional swap device.
Since you mentioned /etc/vfstab above, I'll assume you're running Solaris
and run down the steps for you:

- calculate desired (and available) additional swap space (let's assume

- create a subdirectory under /export/home for your swap file, if you wish
mkdir /export/home/.swapfiles
chmod 700 /export/home/.swapfiles

- create a 64M file for use as swap space
/usr/sbin/mkfile /export/home/.swapfiles/064m-1
(I chose the name in case you later make a 32M or 128M swap file, or a
second 64M swap file. It's actually immaterial.)

- start using the swap space
/usr/sbin/swap -a /export/home/.swapfiles/064m-1

- make the addition permanent
echo "/export/home/.swapfiles/064m-1 - - swap - no -" >> /etc/vfstab

- enjoy your new swap space
Xdoom &"

Matthew Stier <> says.....
"The easiest, fastest, most flexible t hing to do, is to create a swap

In a filesystem you can have available space, use 'mkfile' to create a file
of the size of swap space you want to add, then use 'swap -a' to add that
space to to swap.

The performance penalty, is typically < 1%"
>> END

Opinion was divided between adding a swap file or repartitioning and
increasing the swap partition. Performance issues are, it appears,
negligible between the two. There are plenty of references to this in the
Archives (which I couldn't access at the time of my posting this question).

In the end, I went for repartitioning the disk and restoring /export/home
after rebooting. All went OK.

Many thanks to :

David Thorburn-Gundlach <>
Benjamin Cline <>
Rich Casto <>
Brion Leary <>
Matthew Stier <>
Glenn Satchell - Uniq Professional Services <
Mariel Feder <>

for their invaluable help.

Cheers !

              Bill Walker
        Tel: UK+(0)171 378 5775
    Securities and Futures Authority
            London, England

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