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39671
August 3rd, 2011 11:00
Suggested Cache start end flush settings for MD3200i
Hi;
We are using an MD3200i connected to 4 ESX / HBA hosts - I was wondering if anyone could give advice on the best settings for the cache currently set on the defaults(except 16k)::
storageArray cacheBlockSize=16;
set storageArray cacheFlushStart=80;
set storageArray cacheFlushStop=80;
I'm not sure why is the start and end flush value the same value? and why could they not be increased to 90% for handling the IO load of the 4 servers and many VM's..
Thanks
Aubrey
We are using an MD3200i connected to 4 ESX / HBA hosts - I was wondering if anyone could give advice on the best settings for the cache currently set on the defaults(except 16k)::
storageArray cacheBlockSize=16;
set storageArray cacheFlushStart=80;
set storageArray cacheFlushStop=80;
I'm not sure why is the start and end flush value the same value? and why could they not be increased to 90% for handling the IO load of the 4 servers and many VM's..
Thanks
Aubrey
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itpro44
8 Posts
0
July 29th, 2012 20:00
I second this question... anyone have an answer?
DELL-Kenny K
685 Posts
0
August 1st, 2012 13:00
The block size of 16KB is the recommended setting. As far as the cacheFlushStart and cacheFlushStop, you want to have the stop lower then the start value. I would recommend to either drop the stop to 70 or go ahead and bump up the start to 90. Below is the CLI guide and on pg 263 it starts talking about these settings.
support.dell.com/.../CLI.pdf
I hope this helps. Please let me know if you have any further questions or concerns.
itpro44
8 Posts
0
August 1st, 2012 13:00
Thanks Kenny. I appreciate it. It appears that this controls write caching. As for ready caching, how long does data stay in the read cache? Is that time controllable?
DELL-Kenny K
685 Posts
0
August 1st, 2012 14:00
If you use the following parameter cacheFlushModifier
It sets the maximum amount of time that the data for the VD stays in cache before the data is flushed to physical storage. However to have access to all of these cache flush settings you would have to get the add on premium feature called the High Performance Tier.
Without that premium feature all those settings are not changeable. If you do get that feature here is some information that will help.
www.dell.com/.../high-performance-tier-implementation-guide.pdf
Also if you do get the premium feature you want to be extremely careful when changing the settings as it will affect the entire database. With ESX you may be best to just leave it at 80 and 80 just to be on the safe side.
itpro44
8 Posts
0
August 1st, 2012 15:00
I miss typed the word read in my last post. My fault. My question is regarding the read cache settings. How long does data stay in the read cache, meaning that it doesn't have to get written to the storage, it's just there to speed up future reads. Thanks again.
DELL-Kenny K
685 Posts
0
August 1st, 2012 19:00
The way the read and write cache works is that the data stays in the cache until the cache gets about 80% full and then it is flushed. Unfortunately that threshold is not changable unless you you have that premium service that I had mentioned above. Let me know if there is anything else I can assist you with on this issue.