Intel mbr and lun allignment for Redhat

Question

We just got a new cx3-40 and we will be attaching Redhat/Linux/Dell servers mostly running Oracle 10g. We know about using fdisk to set up our only partition w/a 128 block offset to align the rest of the data blocks. Our practice for Oracle systems has been not to fdisk the drives at all and feed the whole disk to oracle as a raw device. Does this avoid the problem or should we be using a partition w/the 128 block offset?

DaveZ1 · Accepted Answer

Please, do adjust the partition to 128 blocks. Perhaps in the past you ran 'misaligned' and did not notice any performance problems, but if you plan to run the database hard, and want to get the most out of your new system, the offset adjustment will pay off - either in topline IOPS achievable, or in response time. Since this is a change you can only make when no data is on the drives (as it rewrites the partition map) now is the time to do it.

Note this applies to Oracle whether you plan to use ASM or not.

RRR · Answer

How does this array based alignment work out when you decide to start using layered apps, such as MV ? Best Practices are that when you use those, don't use array based alignment, but do host based alignment. And as far as I can read in the question, the lun is a raw device and I'm not sure whether Oracle will make a partition on it or not.

DaveZ1 · Answer

Hi RRR, Sorry, I thought you were referring to FDISK, which is not array-based alignment. FDISK adjust the paritition map. That is the correct approach to take. Use FDISK as explained in the BPG to buffer the parittion map to 128 blocks.

You are right, you do not want to use the "LUN Offset" in Navisphere.

RRR · Answer

Is there any reason why you should use the 'LUN offset' in Navisphere ? Any reason at all ? If not, why not take it out and make it part of the engineering mode or something ? Or a special command line parameter....

DGM3 · Answer

Is there any reason why you should use the 'LUN offset' in Navisphere ? Any reason at all ? It should be useful in any situations where a host operating system may not offer its own alignment capability.Regards,DGM

RRR · Answer

Yeah, but this issue is only on IBM (intel) compatibles, so Windows, Linux, VMware and AFAIK all of those have host based alignment tools available.

dynamox · Answer

not on Egenera (http://www.egenera.com/index.htm)

RRR · Answer

Never heard of.....

CLARiiON

Intel mbr and lun allignment for Redhat

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