Monday, May 24, 2010

Rename file and BAAG

There are two reasons why I'm posting this. First I have read a interview
with Alex Gorbachev
about BAAG and second I run into BAAG related problem myself.
This was not pure BAAG problem as I used my knowledge but I forgot about one very important step - VERIFY old knowledge (based on Oracle 8i) with current release. What I did ?

A scenario was very simple - I have a "production" database (thanks God it was only my VM) running on ASM with all files in group called DATA. I cloned that database using a storage snapshot functionality and then I have renamed ASM group to different name and mounted it. So far so good. Next step was to mount a cloned database and rename a files in control file using old fashion command
ALTER DATABASE RENAME FILE '+DATA\xxxx\redo01.log' to '+DATACLONE\xxxx\redo02.log';
Command was successfully finished and control file has been updated. I have checked a alert log and what was my surprise when I saw warning that file source can't be deleted.
WARNING: Cannot delete Oracle managed file 
I didn't want to delete a source file - this file is a part of source database. It was very interested and I did another test - I have stopped a source database and run rename command for other file.
And ? Yes a source file has been deleted. What if you do it on production environment without test ?
The most worry thing is that latest SQL reference there is no information about that behavior.
This clause renames only files in the control file. It does not actually rename them on your operating system. The operating system files continue to exist, but Oracle Database no longer uses them.
This is not about ASM but if there is a different behavior for ASM it should be mentioned as well.
So there are three important things to remember:
- always check what you are going to do and not guess a results
- check relevant of vendor docs, White papers and other well know stuff with current release of software.


Tuesday, May 11, 2010

Persistent ISCSI disks name

Last few days I was working on Oracle cloning possibility using storage snapshots (post will be blogged soon) and I hit a ISCSI issue at the very beginning.
I have been playing with restarting storage and Linux box and from time to time ISCSI disk has been mapped to different block devices (/dev/sdb1 instead of /dev/sdc1). I really need to keep this persistent and I found this instruction for RedHat Linux (so it should work for OEL and CentOS).
Additionally I was looking for possibility to check how IQN shared on storage is mapped to Linux block devices. There is a nice directory layout where you can check that.
[root@piorovm by-path]# pwd
[root@piorovm by-path]# ls -l
total 0
lrwxrwxrwx 1 root root  9 May 11 13:01 -> ../../sdc
lrwxrwxrwx 1 root root 10 May 11 13:01 -> ../../sdc1
lrwxrwxrwx 1 root root  9 May 11 13:01 -> ../../sdb
lrwxrwxrwx 1 root root 10 May 11 13:01 -> ../../sdb1
lrwxrwxrwx 1 root root  9 May 11 13:00 pci-0000:00:07.1-ide-0:0 -> ../../hda
lrwxrwxrwx 1 root root 10 May 11 13:00 pci-0000:00:07.1-ide-0:0-part1 -> ../../hda1
lrwxrwxrwx 1 root root 10 May 11 13:00 pci-0000:00:07.1-ide-0:0-part2 -> ../../hda2
lrwxrwxrwx 1 root root  9 May 11 13:00 pci-0000:00:07.1-ide-1:0 -> ../../hdc
lrwxrwxrwx 1 root root  9 May 11 13:00 pci-0000:00:10.0-scsi-0:0:0:0 -> ../../sda
lrwxrwxrwx 1 root root 10 May 11 13:00 pci-0000:00:10.0-scsi-0:0:0:0-part1 -> ../../sda1
[root@piorovm by-path]#
When you know which IQN is pointed to which block devices we can use mentioned RedHat instruction with some additional remarks.

Here is output from my configuration
  1. Check WWID for block devices
  2. [root@piorovm ~]# scsi_id -g -s /block/sdb
    [root@piorovm ~]# scsi_id -g -s /block/sdc
  3. Go to
    [root@piorovm ~]# cd /etc/udev/rules.d/
    and create a file called 20-names.rules Replace my WWID with results from scsi_id command and put correct names
    [root@piorovm rules.d]# cat 20-name.rules
    KERNEL=="sd*", BUS=="scsi", PROGRAM="/sbin/scsi_id -g -s", RESULT=="3600144f04be7ffdf00000c2936224200", NAME="sdc"
    KERNEL=="sd*", BUS=="scsi", PROGRAM="/sbin/scsi_id -g -s", RESULT=="3600144f04be80ec000000c2936224200", NAME="sdb"
    Here is a change with RedHat doc – use double equal mark "==" instead of one equal mark "=" for compare (KERNEL, BUS,RESULT).

  4. Save file and start
    [root@piorovm ~]# start_udev
    Starting udev:                                             [  OK  ]
    [root@piorovm ~]#