I've been watching this thread, and I have to agree that I would not use symlinks or mknod. The issues with duplicate entries or mismatched pointers outweigh the advantages.
For unique naming I like the idea of using rendev for hdiskX to hdiskASMX. Beware not to go crazy with renaming. Keep the hdisk prefix and a number at the end.
I've often considered renaming hdisks by LUN ID, but I'm concerned that hexidecimal letters would throw off the device table. I'm sure somewhere there's a regexp of "hdisk[a-zA-Z]*[0-9]+" that something must be using. It'd be neat if a LUN ID (lspv -u) like 332136005076210220092F00000000000035304214503IBMfcp (LUN 0353) were renamed to hdisk0353. On the other hand hdisk03AB might break something.
Regarding lkdev, that's a cool new feature. I read on another site where it wasn't working reliably. I've had poor luck with the chdef command which was introduced about the same time, so I'm not confident in lkdev's reliability. I'd have to test it more.
------------------------------
Russell Adams
------------------------------
Original Message:
Sent: Tue February 22, 2022 08:55 PM
From: Cesar Daniel Delgado Ponce
Subject: Oracle Rac on AIX disk config. Mknod or simboloc links
Ok
Thanks. Valid point. In fact one of the things we always keep documented is that relationship between the hdisk device, the name of the alias for Oracle (for example /dev/asmdiskXXX) and the major and minor numbers. We also use the lkdev command in order to lock the device to help avoiding a rmdev by mistake.
I'm going to test using simbolic links cause i don't know what happen if i deleted the hdisk device with the symbolic link ????. is it deleted ???
Thanks for your comments.
César Daniel Delgado Ponce.
Sistemas Operativos Seguridad Distribuidos (6181)
+58 212 503 0619
Twitter:@MercantilBanco
YouTube: Mercantil Banco
Original Message:
Sent: 2/22/2022 3:58:00 AM
From: José Pina Coelho
Subject: RE: Oracle Rac on AIX disk config. Mknod or simboloc links
Don't use mknod to create the aliases, because if the disks are removed and rediscovered, the mknod entries you've created may be pointing at the wrong disks, and they'll still have the write permissions for oracle.
- Use symbolic links instead.
- Always rename the RAC hdisks to start on a high number. That way, if they're removed and rediscovered they won't be accessible until your script renames them back to the high range, and changes their permissions/ownership. (at 3A.M. it's a lot easier to spot a symlink pointing at a non-existing hdisk1032 than it is to spot a symlink to the wrong hdisk32)
The reason you don't see a performance difference is that opening an mknod /dev/asm32 is the exact same operation as in /dev/hdisk32 (opendev maj, min), and even if you go through a symlink, it's only the open that takes one millisecond longer.
------------------------------
José Pina Coelho
IT Specialist at Kyndryl
Original Message:
Sent: Mon February 21, 2022 12:12 PM
From: Cesar Daniel Delgado Ponce
Subject: Oracle Rac on AIX disk config. Mknod or simboloc links
Well looks like i'll keep working with mknod alias. I'm trying testing I/O performance with nstress tools (ndisk64) but have not seen any important difference.
Thanks for your answer.
César Daniel Delgado Ponce.
Sistemas Operativos Seguridad Distribuidos (6181)
+58 212 503 0619
Twitter:@MercantilBanco
YouTube: Mercantil Banco
Original Message:
Sent: 2/21/2022 9:36:00 AM
From: Norman Owens
Subject: RE: Oracle Rac on AIX disk config. Mknod or simboloc links
I agree with Anker. I've been supporting Oracle RAC on AIX for a long time. I've never used symbolic links. As Anker described, I have the DBA use the /dev/rhdisk devices. Make sure that the disks are owned by oracle:dba and the permissions are set to 660. I have a script that I run when I need to add oracle ASM LUNs. It sets the permissions along with queue_depth max_transfer, reserve_policy and algorithm. I like to keep things simple so that it is easier to troubleshoot issues.
------------------------------
Norman Owens
Open Systems Architect
Mohawk Industries
Original Message:
Sent: Thu February 17, 2022 05:40 AM
From: Cesar Daniel Delgado Ponce
Subject: Oracle Rac on AIX disk config. Mknod or simboloc links
Hi fellows.
We are working with an Oracle consultant deploying a new Oracle Rac cluster of two AIX 7.2 lpars with disk resources from the customer SAN. We have several clusters running on Solaris, AIX and Linux. For Solaris and AIX we have been using the mknod approach of creating mknod alias of each /dev/hdiskX devices to a /dev/asmdiskX devices that will be used by the Oracle ASM to create diskgroups.
Consultant is recommending the use of simbolic links like /dev/asm/asmX to the /dev/rhdiskX device, very much the same as Linux approach using udev rules.
I would like to know if you have any info or experience you may want to share about which approach is better from performance point view. I know using mknod requires some extra work.
Thanks in advance.
------------------------------
Cesar Daniel Delgado Ponce
Systems Specialist
Mercantil Bank Venezuela
Caracas
+584166119255
------------------------------