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August 11th, 2014 10:00
Host I/O Limits
Do any of you have experience with setting Host I/O Limits against an SG? If so would you be willing to share your approach to this and experiences using I/O limits. I have a VMAX 10K and right now I have an AIX host in the TEST environment generating 18K IOPS for the past several hours. We're digging into what is going on with the host since this is 3x what we've seen before but meanwhile I want to consider setting limits to reduce impact to other hosts.
I've read a couple of the EMC whitepapers on I/O limits and what I'm realy looking for is real world experience.
Thanks for any assistance.
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PedalHarder
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August 11th, 2014 15:00
We recently used Host IO limits to resolve a write pending issue. So used the bw_max parameter as this issue was throughput related. It was straight forward to set and check with symsg set and show. We set the bw_max multiple times, lowering the value each time to ensure we got the desired effect without causing a new issue. My advice for you is to do the same. start conservative and change the value in increments.
vic_engle
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August 12th, 2014 07:00
Thanks Jasonc. We'll definitely follow that method.
amit_stg_emc
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August 19th, 2014 01:00
Host IO limit , as the name suggests is used to limit the host IO either via limiting IOPS or bandwidth. In most cases IOPS limitation is good enough . However in some case bandwidth limiting might also be needed.
Use case for HOSt IO limit : IF you provide different class of service to customers like three different class of devices 1st class 2nd class third class then you can limit each kind of device with number of IOPS you think it should do.
This way you restrict the host to not do more IOPS than its supposed to do and affect other hosts.
also keep in mind . Dynamic distribution is important parameter of HOSt IO limit . Make sure you set it to "ALWAYS" . In short makes sure that IOPS are distributed dynamically across different Fa's during performance bottleneck or failure of FA.
lets say there are two Fa's , and you limit the hos tto do 100 IOPS and one Fa fails . If dynamic distribution is not set then single FA will do only 50 IOPS.
Hence this is an important parameter and you should read up on that.