Re: disk I/O problems and Solutions

[Blake Hudson <blake@xxxxxxxx>]

-------- Original Message  --------
Subject: Re: disk I/O problems and Solutions
From: Alan McKay <alan.mckay@xxxxxxxxx>
To: CentOS mailing list <centos@xxxxxxxxxx>
Date: Friday, October 09, 2009 12:55:35 PM

Since you stated that your system is only having trouble at writes,
doing batch inserts, I would look at how you are doing these batch
inserts and see if you can optimize this by using techniques to delay
key writes or adjust locking mechanisms on the insert. Some databases
have special insert from file or bulk insert operations that are much
faster than running many single row inserts - be sure you are taking
advantage of these methods.
    

Yeah, our DB geeks have already said a few weeks ago that they think
we are doing these bulk updates in a pretty inefficient manner, so
that's something else we plan to optimize.


  

I meant to include some annecdotal advice in my last post... In my experience, most of our DB servers rarely access the disk. Though we do configure our db servers for RAID10 now (previously RAID5). RAM is cheap and you should always have plenty of it.

Given your setup, I would be surprised if you would get more than a 100% improvement from transitioning to RAID10 using your current hardware. However, I wouldn't be surprised if you could get a 1,000% to 10,000% improvement through software optimization. This includes proper db software config, db schema, queries, and how you process/prepare data to go in/out of your db.

Keep in mind that if you are disk limited now and top shows no other signs of stress, then you are likely to continue to be disk limited - though you may notice shorter periods of impact.

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