1) add another swap slice, the same size, on a different drive.
     2) or add a file and dedicate it to swap.

   The latter idea is mediocre at best, and the following example will
   describe adding a swap slice.

   Issues to note:
   ----------------
    *  The kernel will distribute the usage of multiple swaps on different
       drives in a stripe style, if the swaps are identical size.
    *  It doesn't fill them sequentially or wait for busy drives.
    *  So we strive for identical sized swap slices.
    *  If the slice can't be identical in size, then larger.
    *  We can always make the swaps identical size in /etc/swaptab (in blocks).
    *  Adding a slice was discussed in Section (How do I list my partition and
       slice layout?  Is there a divvy?).

Here we go:

   --- Adding a swap slice ---
   There are two ways:

   A) When you installed the drive with diskadd then prtvtoc/edvtoc.
      This is kludgey, becasue the disksetup slice adding program
      is not coded to specifcally deal with swap slices.

   B) After the disk is installed, add a swap slice just like you would
      add any other slice, except swap has a 0x3 tag.   I'll describe
      this way, so as to augment (How do I list my partition and slice 
      layout?  Is there a divvy?).  See that section if you need
      to recall how to add a slice, in general.

  Given:
    A Uw71X system with two scsi hard drives on the same controller,
    labeled with id 0, and id 12.  Both drives have one Uw7/OSR6 partition
    that is active.  I know that disk2 slice 180 is free, so I'll use that:
    (It's probably better to use the lower numbers and work your way up,
    but I'd like to illustrate a slice number above 16 and issues like hex
    names and device nodes).

  Solution:
   1)  Determine the exact size and specifications of the swap
       slice on disk1 that we'll duplicate on disk2.

          prtvtoc -p /dev/rdsk/c0b0t0d0s0
          prtvtoc -f /tmp/mytoc /dev/rdsk/c0b0t0d0s0
          cat /tmp/mytoc | grep 0x3

       I know that the TAG for a swap slice is 0x3.  So I can grep
       /tmp/mytoc for that TAG  which shows, with my added titles, that:

       SLICE      TAG      FLAG       START       SECSZ
          2       0x3      0x201      642600      433755

       I see that I'm trying to add a swap slice that's 433755 sectors.

       From the prtvtoc -p I see that disk1 has  1115C, 255H, 63S/T, 512B/S.
       A bit of math (255 * 63) tells me that the Magic Number for a disk1
       cylinder is 16065 sectors.  Now (433755 / 16065) = 27 cylinders.
       And I can calculate that (433755 * 512) = 222082560 bytes.

       So from all this I gather my requirements:

          A)  My new swap slice SLICE = 180.
          B)  My new swap slice TAG = 0x3
          C)  My new swap slice FLAG = 0x201
          D)  My new swap slice START is yet to be determined.
          E)  My new swap slice SECSZ would like to be = 433755
          F)  My new swap slice cylinders would like to be = 27.

   2)  Examine disk 2 and see if I can create that layout.  The big issue
       I'll face is my disk geometries may be different.  I am trying
       to have all swaps the identical size and have all swaps start and
       end on cylinder boundaries.  Here is a head to head comparison of the
       output of the following commands on the two slices:

          prtvtoc -p /dev/rdsk/c0b0t0d0s0
          prtvtoc -p /dev/rdsk/c0b0t12d0s0

           Cyl       Heads    Sec/Trk   Bytes/Sec    Magic Number
          1115        255       63         512          16065
          8748        64        32         512          2048

       Check out the different Magic Numbers (sector size of a cylinder).
       I can't make both swaps the same number of bytes if the second swap
       slice is to end on a cylinder boundary.

       I will get around this by making the new swap slice at least as large
       as the first swap slice, in sectors that means >= 433755.  Then I'll
       make them exactly the same number of blocks in /etc/swaptab.  In this
       area of administration, 1 sector = 1 block = 512 bytes.

       (2048 * 212) = 434176 sectors = SECSZ      <--  Answer.

   3)  Now I'll create the second swap slice.  This involves the procedure
       outlined in Section (How do I list my partition and slice
       layout?  Is there a divvy?) above.  I'll follow that procedure but use
       the values I calculated in this Section, instead:

       To summarize,

           i.  prtvtoc -f /tmp/swaptoc /dev/rdsk/c0b0t12d0s0
          ii.  vi /tmp/swaptoc.
         iii.  My new swap slice  -        SLICE = 180
          iv.  My new swap slice  -        TAG   = 0x3
           v.  My new swap slice  -        FLAG  = 0x201
          vi.  I see that I can start on   START = 821248
         vii.  I showed that my   -        SECSZ = 434176
        viii.  Add slice 180 to swaptoc using values from iii, iv, v, vi, vii.
          ix.  Save /tmp/swaptoc and exit vi.
           x.  edvtoc -f /tmp/swaptoc /dev/rdsk/c0b0t12d0s0

   4)  The second swap slice is created and now I add it to the list of
       devices that swap uses, by adding the block device to the
       /etc/swaptab file and making the exact same block size as the original.
       I used slice 180 on drive 2, and that looks like:

           Raw device           /dev/rdsk/c0b0t12d0sb4
           Block Device         /dev/dsk/c0b0t12d0sb4

       so /etc/swaptab looks like:
       +----------------------------------------------------------------
       | #swapname               offset(in blocks)     size(in blocks)
       | /dev/swap                       0                   -
       | /dev/dsk/c0b0t12d0sb4           0                433755
       |

   5)  Reboot.  Here I thought I was done without a reboot if I just entered
       swap -c to load the /etc/swaptab file, but I got a Device not found
       error.  Low and behold, the raw and block devices for the second
       disk slice 180 were not created after I did the edvtoc.  My first
       instinct was to make the device nodes by hand with mknod, so I did....

            mknod /dev/rdsk/c0b0t12d0sb4 c 7679 436
            mknod /dev/dsk/c0b0t12d0sb4 b 7679 436

       Wrong again!  The devices were made fine, but swap -c still said
       Device not found.  A bit more reading of man vtoc told me that
       the device nodes for slices 1-15 are created, but 16-183 are not,
       unless the slice exists.  This is all done at boot time, so I
       concluded I needed a reboot :-/.  I rm'd the two device nodes I
       had created, rebooted, and everything worked perfectly.

       swap -l  lists the new swap
       swap -l  lists the new swap

         path                         dev       swaplo   blocks     free
         /dev/swap                    7679,2       0     433752    433752
         /dev/dsk/c0b0t12d0sb4        7679,436     0     433752    433752

From the man 1M swap page (This is not recommended)

   It may not always be possible to find an extra slice to solve a swap
   problem. In that case, a file can be used. To create the swap space,
   you need to create a file as big as the intended swap space. It is not
   enough to simply create a zero-length file; it must be as large as the
   intended swap space.

   To do this, you can use the dd(1M) command, as shown in the following
   example (which creates 32MB of swap space):
   dd if=/dev/null of=/swapfile oseek=32 bs=1024k

   Then add the following line to /etc/swaptab:
   /swapfile 0 -

   Then issue this command:
   swap -c

   The system will use the new swap file following the next reboot,
   because swap -c is run from /etc/inittab at system start time.

<mschalit@pacbell.net>
gerberb@zenez.com