Linux-Informix Forum

Re: Raw devices how-to

Posted By: SEAN DURITY
Date: Friday, 20 September 2002, at 11:59 a.m.

In Response To: Raw devices how-to (Sean R. Durity)

The document below was prepared by Damion Reeves, who did not want to post his e-mail address, because he is quite busy. Thanks Damion for a thorough document. I am upgrading a test server to 9.30 and will try to use raw devices.

Creating and Configuring RAW devices with RedHat Linux 7.3 and IDS 9.2x

RedHat Linux and RAW device compatibility:

RAW devices are supported on RedHat Linux 6.0 - 7.3 (the kernel version I used was 2.4.18).

Informix Dynamic Server and RAW device compatibility:

The Informix Dynamic Server Release Notes for IIF.2000 and 9.21.UC3-1 (found in $INFORMIXDIR/release/en_us/0333/) confirms RAW devices are supported.

Note: Unfortunately RedHat Linux 7.3 does not yet support Kernel Asynchronous I/O (KAIO), so support for RAW devices with KAIO is not supported.

Configuration Steps:

During the RedHat installation process you must leave some un-allocated disk space. This is done using Disk Druid or fdisk during the RedHat installation process.

This un-allocated space cannot be mounted, and will be used as RAW chunks later.

After the RedHat installation process, as the superuser (root user) use fdisk to partition the RAW disk as follows:

fdisk /dev/hda

Note: hda represents the IDE hard drive where the un-allocated space was left. This could be hd for a secondary IDE drive, or sd for a SCSI drive.

When executing fdisk /dev/hda a display similar to the following should be shown:

Command (m for help): p

Disk /dev/hda: heads, sectors, cylinder

Units = cylinders of 16065 * 512 bytes

Device Boot Start End Blocks Id System
/dev/hda1 * 1 33 265041 83 Linux
/dev/hda2 34 555 4192965 83 Linux
/dev/hda3 556 1077 4192965 83 Linux
/dev/hda4 1078 1599 4192933 83 Linux

Now create a new partition by chosing the "n" option.

You should be prompted for the starting cylinder and the ending cylinder. Enter the ending cylinder option, or the size of the RAW partition in Mb (eg for a 2048Mb partition use +2048M).

Display the partition table again by chosing the ?p? option. This should show something similar to the following (with the newly added RAW partition shown):

Device Boot Start End Blocks Id System
/dev/hda1 * 1 33 265041 83 Linux
/dev/hda2 34 555 4192965 83 Linux
/dev/hda3 556 1077 4192965 83 Linux
/dev/hda4 1078 1599 4192933 83 Linux
/dev/hda8 2253 3647 2104483 83 Linux

Now exit and write the new partition table by choosing "w".

At this point MAKE SURE YOU REBOOT the system to ensure the new partition table is made active.

Once the system has been rebooted you need to create the raw devices at the Linux level.

Firstly, make sure your IDS/SCIS devices exist:

ls -l /dev/hda[x-y] or
ls -l /dev/hdb[x-y] or
ls -l /dev/sda[x-y} or
ls -l /dev/sdb[x-y]

Where x, y are integers representing your device names for IDS or SCSI hard disks.

eg ls -l /dev/hda[1-8] for the first IDE drive in your system should show output similar to the following:

brw-rw---- 1 root disk 3, 69 May 5 1998 /dev/hda1
brw-rw---- 1 root disk 3, 69 May 5 1998 /dev/hda2
brw-rw---- 1 root disk 3, 69 May 5 1998 /dev/hda3
brw-rw---- 1 root disk 3, 69 May 5 1998 /dev/hda4
brw-rw---- 1 root disk 3, 69 May 5 1998 /dev/hda8

You now need to create the RAW devices using the following command, but take note of which devices have already been assigned to formatted (ext3) filesystems.

raw /dev/raw/raw1 /dev/hda[x] or
raw /dev/raw/raw1 /dev/hdb[x] or
raw /dev/raw/raw1 /dev/sda[x] or
raw /dev/raw/raw1 /dev/sdb[x]

In my example I used:

raw /dev/raw/raw1 /dev/hda8

You will need to change the owner, group and permissions of the newly created RAW device to informix:informix if the RAW device is to be used as a dbspace/chunk within the Informix instance:

cd /dev/
chown informix:informix /dev/hda
chmod 666 /dev/h

cd /dev/raw
chown informix:informix /dev/raw/raw
chmod 666 /dev/raw/raw

In my example I used:

cd /dev/
chown informix:informix /dev/hda8
chmod 666 /dev/hda8

cd /dev/raw
chown informix:informix /dev/raw/raw1
chmod 666 /dev/raw/raw1

Now verify the devices are defined as RAW using:

raw -qa

This should show output similar to the following;

/dev/raw/raw : bound to major , minor

In my example the output showed:

/dev/raw/raw1: bound to major 3, minor 8

Now check the ownership and permission details of the RAW devices using:

ls -lrt /dev/raw/raw

In my example the command "raw -qa" shows a binding for the /dev/raw/raw1 device to the number major 3 and minor number 8 (/dev/hda8) device:

crw-rw-rw- 1 informix informix 162, 1 Oct 4 1999 /dev/raw/raw1

Now edit the /etc/sysconfig/rawdevices file and add an entry for each RAW device.

In my example I added:

/dev/raw/raw1 /dev/hda8

Re-boot the system again and then type "raw -qa" and you should see the RAW devices, and their major and minor numbers displayed.

Now to allow Informix Dynamic Server to use the RAW devices you simply need to create a link to point to the RAW device using:

ln -s /dev/raw/raw

In my example I used:

ln -s /dev/raw/raw1 /var/informix_raw_chunks/rootdbs

When setup of the RAW devices has been completed it is a simple case of using the Informix ?onmonitor? utility (or the vi text editor) to modify the configuration settings within the $INFORMIXDIR/etc/onconfig. file, then initialise your database instance for the first time.

After this step add/create any new/additional Informix dbspaces/chunks you require.

Messages In This Thread

• Raw devices how-to
  Sean R. Durity -- Wednesday, 18 September 2002, at 3:26 p.m.
  • Re: Raw devices how-to
    SEAN DURITY -- Friday, 20 September 2002, at 11:59 a.m.
    • Re: Raw devices how-to
      SEAN DURITY -- Friday, 20 September 2002, at 4:51 p.m.

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