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Host IO Limits on Unity 600F storage

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Can any help me with the usage of Host IO Limits on Unity 600F..what are the pros/cons ?

Does it make sense to apply Host IO Limits for test/dev environments sharing the same storage with Critical applications ?

Do we need to set the threshold based on IOPS or Bandwidth ?

Are there any best practices to follow while implementing Host IO Limts ?

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Re: Host IO Limits on Unity 600F storage

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I forgot to add a comment on the note above, the system you describe is a Unity 600F, which is currently the highest Unity model, so it would take a very intensive test/dev environment to cause a noticeable impact on the rest of the storage resources. Just my personal opinion though.

Andre @ Dell EMC
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Re: Host IO Limits on Unity 600F storage

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Hi deepz

I don't think there are best practices around host IO limits as these are totally up to the customer and the choices will depend on specific environments.

Does it make sense to apply Host IO Limits for test/dev environments sharing the same storage with Critical applications?

Answer: yes, this might be a good idea if you are worried the test environment may negatively impact the production side of the environment. The downside would obviously be if the test folks need more juice form the array they will be throttled.

Another option would be to use snaps or clones (arriving in Unity OE 4.2) for testing.

IOPS or Bandwidth are 2 metrics used to limit or throttle host activity, but there are some slightly different options.


There is a lot of info on Host IO limits in the Unisphere help menu. Go to performance > host IO limits, then hist the question help at the top right corner.

There is also some info on doc "EMC UNITY: INTRODUCTION TO THE UNITY PLATFORM":

HOST I/O LIMITS

The ability to limit the amount of I/O activity that is serviced by the Unity system is known as Host I/O Limits. Host I/O Limits can be applied on LUNs, VMware VMFS Datastores, and their associated snapshots. Use Host IO Limits to limit incoming host activity on the basis of IOPS, Bandwidth, or both. Limits can be enforced on individual resources, or a limit can be shared amongst a set of resources. There are a number of use cases where Host I/O Limits can be effective. Configure Host I/O Limits on LUNs or datastores that are consuming a large portion of the system’s resources and reducing the performance of other resources on the system. This could be the result of “noisy neighbor” who overruns the provisions set for the multiple tenants accessing data on a system. Another use case for Host I/O Limits is placing limits on snapshots. In the event that attached snapshots are being used for backup and testing purposes, Host I/O Limits can be applied to the snapshots to effectively prioritize host activity towards the parent LUNs and datastores. In UnityOE 4.1, density based Host I/O Limits can be created which limits host activity based on the size of the block resource. For example, a density based I/O limit of 100 IOPS/GB for a 200GB LUN would result in an overall limit of 20,000 IOPS for the entire LUN. If sometime later the 200GB LUN was expanded to be a 250GB LUN, the I/O limit would automatically update to 25,000 IOPS for the LUN, saving the administrator managerial tasks and time. Like absolute I/O limits, density based I/O limits can also be shared among multiple resources. Another feature in Unity OE is burst policies for Host I/O Limits. This option is available for any Host I/O Limit policy and allows host activity/traffic to exceed the base policy limit by a user-specified percentage. The user specifies parameters of amount (percentage), duration, and frequency of the I/O limit burst allowance.

Andre @ Dell EMC
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Re: Host IO Limits on Unity 600F storage

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Thanks Andre,

Appreciate your quick response.

We are not using snapshots for backup/testing hence to leverage this feature i would first need to find out which LUNs are consuming more bandwidth/IOPS. While creating dashboards in Unity, it does not tell me this info on which Storage LUNs are consuming most system resources (may be i am looking at wrong place).

Is there a standard practice to benchmark how many IOPS/GB like you mentioned above 100 IOPS/GB ?

Do you have any idea if other customers have deployed this feature and how has it helped them?

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Re: Host IO Limits on Unity 600F storage

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Hi Deepz,

In the performance dashboards, you can create custom views, for example: select your LUNs and then select IOPS, this will produce a graph with all your LUNs and show the IO for each, here you can look for the ones that may stand out for running more IOPS than they should.  The same can be done by bandwidth.

I think if you are only worried about the test activities harming production, you have to make a decision on how much IO or BW you are willing to allocate to the test environment without causing any harm to the prod part of the environment.

Once you find this value, then you can create host IO limits for those dev/test LUNs.

I don't know your specific environment and therefore it is not clear to me what you mean by"test/dev environments sharing the same storage with Critical applications". If you have the same LUNs shared for both environments, then Host IO limits won't help as these are set on LUNs and not hosts. So in this case if you limit the IO on a LUN, then both test and prod would be affected by the limit.

If however, by shared, you just mean that the dev/test LUNs and the prod LUNs are on the same pool, then host IO limits might be an option. But again the secret is defining the values, and this is not something I can help with as I wouldn't know the environment. There are no set values or guidelines for this as it would depend on each specific setup / environment.

If you are worried about possible impact, then you can also create different pools for different environments. This way the workloads would be entirely separate and should not impact each other.

This is only generic advice as I don't know the environment. If you require more in depth advice, then we have dedicated teams that can assist with this kind of advice. These teams can be engaged via your Dell EMC account team.

Andre @ Dell EMC
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Re: Host IO Limits on Unity 600F storage

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I forgot to add a comment on the note above, the system you describe is a Unity 600F, which is currently the highest Unity model, so it would take a very intensive test/dev environment to cause a noticeable impact on the rest of the storage resources. Just my personal opinion though.

Andre @ Dell EMC
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Re: Host IO Limits on Unity 600F storage

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Hi Andre,

We understand that we have the best Unity storage however we were trying to leverage this feature of Host IO Limits if at all we can else just let them share a single pool and later enable it if needed.

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Re: Host IO Limits on Unity 600F storage

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I understand. Host IO limits can be be useful, no doubt. I hope you don't ever need to used them on your Unity 600F, but if you do, they are easy to setup on Unisphere and with those one environment won't negatively impact the other.

Andre @ Dell EMC
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