Taking Disk Cylinders From Swap on Solaris 8

Kids… DO NOT TRY THIS AT HOME! If this is not done exactly right, you will render your system unbootable and corrupt your data. That being said, under some circumstances you can take some space from your swap partition and add it to an unused one without initializing your entire disk. This is particularly useful if you decide you want to use DiskSuite to mirror your system disk, but have not allocated the 100MB partition that is needed to hold the state databases. As always, BACK EVERYTHING UP FIRST. Better yet, make two backups and store them on two different systems. This is a risky procedure, and you don’t want to lose any data!

You can also use my instructions for copying a Solaris boot drive to a disk with a different partition layout as a safer alternative.

The first thing you need to do is figure out if your disk layout will allow for this procedure. Usually the swap partition is the second one on the disk, making it partition number 1 (Partition number 0 is root). If partition number 1 is swap on your system, and partition number 3 or 4 are unused, you are in good shape, and this should work. To figure this out, you should do something like this:

# format
Select the boot disk – usually disk 0
Specify disk (enter its number): 0
format> partition
format> print

This will show you the current disk layout.


Current partition table (original):
Total disk cylinders available: 24620 + 2 (reserved cylinders)

Part      Tag    Flag     Cylinders         Size            Blocks
  0       root    wm       0 -   725        1.00GB    (726/0/0)    2097414
  1       swap    wu     726 -  9436       11.90GB    (8635/0/0)  24946515
  2     backup    wm       0 - 24619       33.92GB    (24620/0/0) 71127180
  3 unassigned    wm       0                0         (0/0/0)            0
  4 unassigned    wm       0                0         (0/0/0)            0
  5        usr    wm    9437 - 10888        2.00GB    (1452/0/0)   4194828
  6        var    wm   10889 - 18148       10.00GB    (7260/0/0)  20974140
  7 unassigned    wm   18149 - 24619        8.91GB    (6471/0/0)  18694719

Here we see that partitions 3 and 4 are unused and directly after partition 1, so we can take some space from swap and assign it to one of these. Partition 2 is, of course the entire disk. I have not tried it, so I don’t know if you could assign non-sequential cylinders to a partition that is not directly after swap.

So to take some space from partition 1 and add it to partition 3, the first thing we have to do is disable swap, so the format utility will let us change it.

Comment out the following lines in your /etc/vfstab file and reboot the system.


#/dev/dsk/c1t0d0s1         -       -               swap    -       no      -
#swap    -       /tmp    tmpfs   -       yes     - 

This will bring the system up without swap enabled. You can now edit the disk label. Remember that our cylinders need to be sequential, so always work in cylinders when using the format utility.

Re-enter the format utility, select your system disk and view the partition table:

# format
Select the boot disk – usually disk 0
Specify disk (enter its number): 0
format> partition
format> print

Again we wee that partitions 3 and 4 are unused.


Current partition table (original):
Total disk cylinders available: 24620 + 2 (reserved cylinders)

Part      Tag    Flag     Cylinders         Size            Blocks
  0       root    wm       0 -   725        1.00GB    (726/0/0)    2097414
  1       swap    wu     726 -  9436       11.90GB    (8635/0/0)  24946515
  2     backup    wm       0 - 24619       33.92GB    (24620/0/0) 71127180
  3 unassigned    wm       0                0         (0/0/0)            0
  4 unassigned    wm       0                0         (0/0/0)            0
  5        usr    wm    9437 - 10888        2.00GB    (1452/0/0)   4194828
  6        var    wm   10889 - 18148       10.00GB    (7260/0/0)  20974140
  7 unassigned    wm   18149 - 24619        8.91GB    (6471/0/0)  18694719

The first thing we need to do is take some cylinders away from partition 1. In this example, we are looking to make partition 3 roughly 100MB, so we need to take about 75 cylinders from partition 1 so that we can add it to partition 3. Parititon 1 ends at cylinder 9436, so we need to subtract 75 from that number. 9436 – 75 = 9361, so that is the new ending cylinder for partition 1. We then subtract the beginning cylinder (726) from that number to give us the new total number of cylinders for partition 1. 9361 – 726 = 8635, so this is the number we enter when format asks for the size of the partition. Like so:


partition> 1
Part      Tag    Flag     Cylinders         Size            Blocks
  1       swap    wu     726 -  9360       11.90GB    (8635/0/0)  24946515

Enter partition id tag[swap]: 
Enter partition permission flags[wu]: 
Enter new starting cyl[726]: 
Enter partition size[24946615b, 9436c, 12880.92mb, 12.00gb]: 8635c
partition>

Now we have to add these 75 cylinders to partition 3.


partition> 3
Part      Tag    Flag     Cylinders         Size            Blocks
  3 unassigned    wm       0                0          (0/0/0)            0

Enter partition id tag[unassigned]: 
Enter partition permission flags[wm]: 
Enter new starting cyl[0]:9361
Enter partition size[0b, 0c, 0.00mb, 0.00gb]:75c
partition>

Print out the new partition table to make sure everything lines up correctly:


partition> print
Current partition table (original):
Total disk cylinders available: 24620 + 2 (reserved cylinders)

Part      Tag    Flag     Cylinders         Size            Blocks
  0       root    wm       0 -   725        1.00GB    (726/0/0)    2097414
  1       swap    wu     726 -  9360       11.90GB    (8635/0/0)  24946515
  2     backup    wm       0 - 24619       33.92GB    (24620/0/0) 71127180
  3 unassigned    wm    9361 -  9436      107.21MB    (76/0/0)      219564
  4 unassigned    wm       0                0         (0/0/0)            0
  5        usr    wm    9437 - 10888        2.00GB    (1452/0/0)   4194828
  6        var    wm   10889 - 18148       10.00GB    (7260/0/0)  20974140
  7 unassigned    wm   18149 - 24619        8.91GB    (6471/0/0)  18694719

Partition 1 ends at cylinder 9360, and partition 3 picks right up at cylinder 9361. Partition 3 ends at cylinder 9436, and partition 5 begins at cylinder 9437. Partition 4, of course, remains unused. Since none of the cylinders overlap, we can go ahead and write the disk label out. DO NOT DO THIS if you have any doubt at all about what you have just done. By writing out the disk label, you could corrupt the data on your formated filesystems if any cylinders overlap into them. The format utility is usually pretty smart about keeping you from making mistakes, but be very careful anyway! You don’t want to end up with scrambled eggs on a disk that has valuable data on it.

partition> label
This writes out the disk label, so you can now exit the format utility and re-enable swap in your /etc/vfstab file. Simply uncomment out the following two lines and reboot the system.


/dev/dsk/c1t0d0s1         -       -               swap    -       no      -
swap    -       /tmp    tmpfs   -       yes     -

Reboot your system, and if all goes well, it will come up, and you will see that partition 3 will have a little over 100MB on it. Usually people want to do this so they can store the DiskSuite meta database on the newly created partition. If this is the case for you, you can now move on to mirroring the system disk.

Rebuilding the Solaris Device Tree

If you ever shift around any bootable drives within a Sun Solaris box, you may find that either the device names (cxtxd0sx) do not follow the disk position within the server, or, the system just fails to boot because it can’t mount the other disk slices.

Let’s assume you are booting off of target 8 (c1t8d0s0), but wish to move that disk to the appropriate slot to make it target 0 (c1t0d0s0). You have changed all references in the /etc/vfstab file to reflect the new disk position, physically moved the drive from the target 8 slot to the target 0 slot, and changed the boot-device variable within the OBP to the appropriate disk. You should now be all set to boot from the disk in target 0, right?

Not quite yet.

Solaris creates a device tree with links to all the disks it knows about, and these don’t get rebuilt upon reboot. If you simply tried to boot the disk now in target 0, it would find the kernel, but fail to mount any of the other filesystems, because these device links are still pointing to the disk slices on target 8.

In order to boot off the drive in the new position, you will have to remove these device links and rebuild them. Here is how we do that:

1. Insert a Solaris 8, 9 or 10 cd into the hosts cdrom

2. From the ok prompt, enter boot cdrom -s

ok> boot cdrom -s

3. fsck the boot disk

# fsck -y /dev/rdsk/c1t0d0s0

Remember that your boot disk may differ than the example above. Since in our example above, we have put the disk into the slot for target 0 (c1t0d0), that is what we are using here.

4. Mount the root slice on /mnt

# mount /dev/dsk/c1t0d0s0 /mnt

Note that your root slice may differ than the above example.

5. Move path_to_inst

# mv /mnt/etc/path_to_inst /mnt/etc/PATH_TO_INST_ORIG

6. Remove all old device links

# rm /mnt/dev/rdsk/c* ; rm /mnt/dev/dsk/c* ; rm /mnt/dev/rmt/* ; rm
/mnt/dev/cfg/c*

7. Rebuild path_to_inst and devices

# devfsadm -r /a -p /mnt/etc/path_to_inst

8. Unmount the root slice and reboot

# umount /mnt ; init 6

You should now be able to boot off your old drive in its new slot.

What The Heck is RAID 10?

Earlier this month, a company came along and asked for a RAID 10 array. Understanding that RAID 10 is a cooler sounding way of saying RAID 1+0, I understood it as a mirror set that is striped across another mirror set. Simple enough… Just concatenate a couple of mirrors, and you’ve got RAID 10.

Indeed, RAID 10 is simply one or more RAID 1 arrays (mirrored sets) striped together (RAID 0).

RAID 1 creates an exact copy (or mirror) of all of data on two or more disks, while RAID 0 splits data evenly across two or more disks with no parity information for redundancy. By combining the two into a RAID 10 array, you are able to take advantage of the faster write speed offered by RAID 0, while protecting your data against drive failures with mirroring.

This method of RAID is pretty costly, but useful if you find yourself in a situation where you need a lot of throughput combined with a lot of data protection.

Problems With Multiple MetaDB Partitions

UPDATE TO “Solaris Disk Partition Layout & Mirroring Scripts

Several Months ago, I tried to use my old mirroring scripts on a new Solaris 9 install. I found that the the kernel would panic upon reboot because it was unable to mount /. I tried many things, including opening a support call with Sun. They reviewed my scripts and said that they should work, but despite repeated tries, they did not.

In the end, I created only one metadb partition instead of two, and found that the system would boot. I attributed this to a problem with the mirror disk, until it happened to me again this week. For some reason, the implementation of Disk Suite on Solaris 9 does not accept multiple metadb partitions.

Previously, in Solaris 8, I always created a total of four metadb partitions. Two on each drive…

#!/bin/sh
#Mirrorme.sh
prtvtoc /dev/rdsk/c1t0d0s2 | fmthard -s – /dev/rdsk/c1t1d0s2
metadb -a -f -c3 /dev/dsk/c1t0d0s3 /dev/dsk/c1t1d0s3
metadb -a -f -c3 /dev/dsk/c1t0d0s4 /dev/dsk/c1t1d0s4

Currently, with Solaris 9, that method does not work, and results in a kernel panic. To resolve this issue, you must create only one metadb partition on each disk. I’ve been using s3 for this, although you could use any slice you wish.

#!/bin/sh
#Mirrorme.sh
prtvtoc /dev/rdsk/c1t0d0s2 | fmthard -s – /dev/rdsk/c1t1d0s2
metadb -a -f -c3 /dev/dsk/c1t0d0s3 /dev/dsk/c1t1d0s3

Aside from this change, the mirroring scripts continue to work. Please let me know if you find any other problems not mentioned.