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Oracle 10g and SAN volumes

 
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Darrell G
New Member

Oracle 10g and SAN volumes

Here at my current job we are starting a project to move JDE to a new HP-UX server, and in the process upgrading to Oracle 10g.

I've been out of the HPUX/Oracle world for a while and back in those days we used RAW volumes and direct attached storage. Fast forward a few years - now everyone uses SAN and seems to love filesystems to hold Oracle databases.

So this leads me to question a couple things (I don't like to "follow the crowd". I tend to ask "why" and try to do things the right way for the given situation).

1) All of our database volumes are mangaged by the SAN. All the mirroring, striping, etc, is done there. So - why do I need to use LVM of VxVM to manage these volumes? It seems like its just an extra layer of overhead that I simply don't need. So does anyone see any downside to skipping LVM or VxVM and allowing the SAN to manage the volume?

2) I hate to bring up RAW - I know how contentious it is. But the argument against RAW because it is "hard to manage" just doesn't work for me. If its better, then its your job to figure it out. I know a lot of people use RAW for performance reasons, but to me RAW seems better because Oracle now has direct control of what is written to the volume, and when it is written. Its been a while, but back in the day I was pretty sure Oracle recommended raw volumes over filesystems because data integrity could be guanteed better in a RAW volume - because Oracle does ALL the IO. Data integrity is really important to me. I can always make things run faster, but outages are just not acceptable. So are RAW volumes better from an integrity standpoint?

14 REPLIES 14
Jash_1
Frequent Advisor

Re: Oracle 10g and SAN volumes

Darrell,

Glad to have you back to the hpux/oracle scene!

We use both raw and cooked filesystems for our oracle databases here. It is a lot easier to use raw files if you have 11i v3, as any multi-pathing to the luns is automatically taken car of by the operating system. If you are using non HP san disks then multi-pathing can be a real issue with raw partitions, hence cooked is easier.

Just my humble opinion, hope all goes well.

Jash
If I can, I will!
Steven E. Protter
Exalted Contributor

Re: Oracle 10g and SAN volumes

Shalom,

1) You are better off managing mirroring on the SAN. LVM is used to create raw disk areas unless you use Oracle ASM services which puts disk management in Oracles hands. Bad idea ASM.

2)We create soft links to make raw disk areas visible to the root and oracle user. Managing raw disk areas is not a big deal, it merely in this case requires the use of oracle utilities.

Raw disk volumes offer slightly (less than 5%) improvement in performance. Some product like Oracle 10g RAC require raw disk areas.

There is no difference in data integrity between raw disk and cooked file systems when using oracle. Reliability is exactly the same.

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Steven E Protter
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Yogeeraj_1
Honored Contributor

Re: Oracle 10g and SAN volumes

hi Darrell,

i suggest that you also have a look at Oracle ASM.

Worth it!

kind regards
yogeeraj
No person was ever honoured for what he received. Honour has been the reward for what he gave (clavin coolidge)
Oviwan
Honored Contributor

Re: Oracle 10g and SAN volumes

hey

1) with lvm you are more flexible to add more pv etc...

2) check this metalink note: 578455.1 in oracle 12g raw devices are de-supported...

regards
Darrell G
New Member

Re: Oracle 10g and SAN volumes

I agree that using the SAN to manage volumes is better. Adding a volume or any of the LVM related things are handled there, invisible to the OS.

This is the first I have heard of RAW volumes not being supported in the future. That would seem to be a very big change -I'm sure a lot of people are hating that.

I have seen conflicting opinions on ASM, some say it great, others hate it. What are the issues with ASM? I can't see that ASM really gives me anything. I don't have a cluster, and the SAN takes care of balancing any IO.

Multipathing to the SAN could be an issue, but we plan to use port agregation to overcome the multipathing issues in 11.23. It is a method supported by our SAN, so should work.



Darrell G
New Member

Re: Oracle 10g and SAN volumes

We have decided to go with ASM, but this brings a whole new question.

ASM provides a lot of fucntionality such as striping, mirroring, load balancing, etc. BUT, these are the exact same things already done by the SAN. It makes little sense to me to let ASM stripe and load balance, then send all this data off to the SAN have it do the same. And certainly the SAN will do this process much more efficiently that ASM could and not use my CPU cycles for disk management.

So can these things be disabled in ASM?

I also note that Oracle recommends multiple drives for performance. But in our case, we have two aggregated lan adapters going to one SAN - so one path to one device. Do we really gain anything by having mulitple LUNS when they all go to the same SAN via the same path? We are only talking about 1TB of data, so is there a real difference between one 1TB LUN or four 250 GB LUNS?

One Admin here has concern about the I/O queueing because he feels that a single large LUN will have queue contention. But we have a SAN with a huge number of spindles behind it, so how much is I/O queueing going to play into this?
Deepak Kr
Respected Contributor

Re: Oracle 10g and SAN volumes

>>there a real difference between one 1TB LUN or four 250 GB LUNS?

Yes, we had same concern in the past while implementing ORacle 10g RAC cluster.

Finally we took muliple luns instead of a large big lun from SAN Box...

For ASM multiple luns will do better.
"There is always some scope for improvement"
Oviwan
Honored Contributor

Re: Oracle 10g and SAN volumes

Hey

when you create a diskgroup in asm you can tell asm what kind of redundancy you want. In your case you should use "external". check this:
http://download.oracle.com/docs/cd/B28359_01/server.111/b28286/statements_5008.htm#SQLRF01114

Maybe you can displace some bottlenecks if you use four 250GB Lun instead of one 1TB lun.

Regards
Solution

Re: Oracle 10g and SAN volumes

Darrel,

This has been a very "vanilla" conversation so far, but if you want to get into the whys and wherefores of ASM, to give some real advice we're going to need to know a bit more about your SAN... You seem to indicate you have 2 HBAs attached to your SAN, but what sort of storage is it? HP EVA? HP XP? EMC Clariion? EMC DMX? These specifics start to make a lot of difference when deciding how to configure your LUNs on the host.

As to concerns about queueing - yes there can be issues - each LUN has a SCSI queue associated with it which contains all the outstanding IOs to that LUN. The default queue depth on HP-UX is 8, so if you only use 1 LUN by default you will only ever have a maximum of 8 concurrent IOs outstanding at any point in time (most disk arrays can manage a lot more than that!) - if you have 8 LUNs, you can have 64 concurrent IOs outstanding. Of course this queue depth can be tuned if you need to.

Tell us a little more about your environment and we should be able to make some better recommendations for you.

HTH

Duncan

I am an HPE Employee
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