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Reconfiguring FAST Cache
I just received some more EFD's and I like to reconfigure the FAST Cache. Today, it's configured with 4x200GB on a cx4-480. I'll be adding another 4 and capitalize on the max of 800GB of FAST Cache. My questions are:
1. Are there any prerequisite when deleting the existing fast cache configuration? If i'm not mistaken, system cache will be temporarily be disabled?
2. how much of the system cache will be used up with a max of 800GB fast cache on a cx4-480?
3. are there any configuration changes need to be made on the system cache such as changing the Read/Write ratio of the system cache? I think we employ an 80\20 percent rule (write\read).
thanks!
1637
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Posted July 12th, 2011 06:00
I suspect i would have to minimize IO traffic when performing the FAST Cache configuration because it system cache gets disabled?
1338
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Posted July 12th, 2011 06:00
2 - 3. I estimate you'll have 1709 MB or there abouts. It may be lower depending on what else you have installed. The read/write cache ratio shall be maintained through the addition. However, you may want to consider a 1368 MB write and 341 MB read cache, if that's not what you see.
1637
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Posted July 12th, 2011 14:00
tkjoffs - there is no reason why you would have to go through all your "FAST enabled LUNs" because you are reconfiguring your FAST Cache. Why did you think you would have to do that? If there is any documentation which mentions that, let us know so that we can get it corrected.
1637
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Posted July 12th, 2011 14:00
Yes, since you are disabling FAST Cache for some time, you should plan to reconfigure the FAST Cache during a low activity period.
1637
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Posted July 12th, 2011 15:00
You should also look at distributing the EFD disks across the back-end buses - don't put the disks all on one bus - you could overload it.
glen
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Posted July 12th, 2011 17:00
I was under the impression that if you destroy your Fast cache it will disable it on the existing LUNs. Hence the same would apply as if you are installing a FAST cache for the first time - anything provisioned before it is configured would be disabled by default???
If not, even better.
1393
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Posted July 12th, 2011 20:00
just destroyed fast cache on my 5700, fast cache option remained available and checked on LUNs.
670
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Posted July 12th, 2011 20:00
you could try your friendly EMC account rep
1393
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Posted July 12th, 2011 20:00
Thanks! Nice to know. Okay, where can I get a lab array? Free hopefully…. J
tkjoffs
159 Posts
1637
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Posted July 11th, 2011 21:00
1 - You assumptions here are correct, this will stop FAST Cache and System Cache during the re-configuration.
2 - The percentage of memory overhead for FAST Cache is used for the memory map and is allocated in 64k chunks. This scales in a linnear fashion, so if you are scaling exactly double, you should expect to see double the hit on space.
3 - Should not need to modify the config for the standard cache.
Please note, that if you disable and re-enable FAST, you will have to go back through all your FAST enabled LUNs and re-enable them to use FAST again I believe.