Change device - block to character

[Pat Shea_1]

First, I'm a DBA so apologies for any incorrect/incomplete terminolgy. We have a 4 node Tru64 cluster with SAN storage using cluster file systems (CFS). We're adding more storage as raw devices and I'll put the current 10g databases on ASM. I will upgrade several other databases to 10g/ASM in the near future. I've asked our Unix admins if they can change (from block to character) the storage that I'll "vacate" with the first move to ASM. Or will I need to justify buying new storage? They haven't been able to give me an answer yet. Can you provide any information?

[Hein van den Heuvel · Accepted solution]

There is no such thing as converting a character device to a block device.

The devices are avaible both ways.

You currently probably have files sets in domains on disks, with their mountpoints for example /dev/disk/dsk2 --> oracle_domain --> system_fileset ---> /ora/sys

As you no longer need that, you can choose to give /dev/rdisk/dsk2 to Oracle ASM to play with.

However, yo may want to take the opportunity to review and possibly redo the SAN disk assignments.

Carefully read and re-read the Oracle / ASM / Tru64 manual.

For furhter help it may help to talk in concrete example. Please provide a (partial) output from 'df' and maybe 'hwmgr -show scsi'.

Good luck!
Hein.

[Ivan Ferreira]

Every Unit on the operating system (disk) have two access mode, block and character (RAW). So, for example, if you have one file system called /oradata, this file system is created on the disk /dev/disk/dsk1c.

If you destroy the data on the file system you can use the disk as a raw device, accessing via /dev/rdisk/dsk1c special file.

Block devices are located in /dev/disk and character devices are located in /dev/rdisk.

[Pat Shea_1]

Thanks to all for your replies. I probably should have asked if there were any concerns/criteria/"gotchas" for changing the access method. I'm aware that I can access either via different /dev/ paths. But, for example, should the Unix admins remove the entries from /etc/fstab, does it matter if the system mounts the file system. Oracle should be the only app that accesses those devices but I'd want to prevent any "accidental" access. I don't know what I don't know so I may not be asking all the right questions.

[Ivan Ferreira]

The unix admins should remove the file systems on the device, remove the entries from fstab to ensure that the device won't be used as block device anymore. It must not be mounted, and yes, Oracle should be the only app that accesses those devices but I'd want to prevent any "accidental" access.

[Arch_Muthiah]

Pat,

A DRD (Device Request Dispatcher) subsystem controls all I/O to physical devices. The DRD facility provides highly available clusterwide access to both character and block disk devices, as well as tape devices, to all cluster members, regardless of where the storage is phisically located in the cluster.



Archunan

[Pat Shea_1]

Thanks for all the help