topic Re: how to use raw devices in Operating System - Linux

how to use raw devices

Maaz — Fri, 19 Sep 2008 06:07:21 GMT

# cat /etc/raw
raw1:sda5
raw2:sda6
raw3:sda7

# raw -qa
/dev/raw/raw1: bound to major 8, minor 5
/dev/raw/raw2: bound to major 8, minor 6
/dev/raw/raw3: bound to major 8, minor 7

# ls -l /dev/raw/
total 0
crw-rw---- 1 root disk 162, 1 Sep 19 13:00 raw1
crw-rw---- 1 root disk 162, 2 Sep 19 13:00 raw2
crw-rw---- 1 root disk 162, 3 Sep 19 13:00 raw3
crw-rw---- 1 root disk 162, 0 Sep 19 13:00 rawctl

# ls -l /dev/sda5
brw-r----- 1 root disk 8, 5 Sep 19 08:16 /dev/sda5

# ls -l /dev/sda6
brw-r----- 1 root disk 8, 6 Sep 19 08:16 /dev/sda6

# ls -l /dev/sda7
brw-r----- 1 root disk 8, 7 Sep 19 08:16 /dev/sda7

now I wana access the raw device
# mount /dev/sda7 /mnt
mount: you must specify the filesystem type

why ? /dev/sda7 is a raw device, why should I make a filesystem on the RAW device(/dev/sda7) ?
I have heard that:
raw device doesnt require filesystem.. thats why these devices provides fast I/O, because there is no filesystem layer b/w application and the device.

Regards

Re: how to use raw devices

Sandeep_Chaudhary — Fri, 19 Sep 2008 10:45:45 GMT

dont try to mount raw device
iof ur RAW DEVICE is paret of VG u have to activate VG. I use raw device for oracle database on HP-UX. when u are using mount command means u r working with filesystem. Thats why u r getting the error.

Re: how to use raw devices

Ivan Ferreira — Fri, 19 Sep 2008 14:25:40 GMT

Raw devices are mapped in /etc/sysconfig/rawdevices. They are used by products like Oracle database and they access directly to these devices without a file system on it. Without a product like a database, raw devices are not useful for you.

Re: how to use raw devices

Jeeshan — Mon, 22 Sep 2008 16:21:01 GMT

yes, you cannot mount a raw device. actually without creating file system you cannot mount any disk devices.

Oracle or specific applications have the special considerations to read/write in the raw devices.

Re: how to use raw devices

Jeeshan — Mon, 22 Sep 2008 16:22:06 GMT

you can check the raw device file using command stat

#stat -f /dev/sda7