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October 6th, 2014 07:00

How does FAST move the extent?

Hello Experts!

Could you please tell me how it can be according next output if we have the FAST policies like this:

Policy A:    10% EDF - 10 % FC - 80% SATA

Policy B:     15% EDF - 15 % FC - 70% SATA

and output:

Screenshot002.jpg

the device 09c1 and 061e are bound to SATA pool and as you can see the extents are allocated on SATA and EDF only?

How is it possible? We have strong rules for FAST and as I understand all extent should be allocated according these rules:

(for Policy A) - 10% extents should follow to EDF, 10% to FC and 80% to SATA respectively. On the screen shot I don't see allocation for FC pool at all. Could you please explain?

And one more question regarding pools and FAST.

For instance we have 3 pools - EDF, FC and SATA. and free space on them EDF - 1 gb, FC - 5 gb and SATA - 100gb.

and the same FAST policy - 10% EDF - 10% FC and 80% SATA.

I bind new volume 100gb to FC pool (Max. Subscription limit allows me to do that and don't think about PRC for this example) and host does write to volume and within 10 min all 100 GBs have been written to volume. Of course almost all of extents will be written to SATA pool (am I right?) and then how the FAST will transfer extents if we have so strong policy? it can allocate 10 gb on EDF and 10 gb on FC pools, there are not enough space. which is the behavior of  FAST in this situation?

Thank you!

Message was edited by: evgenym

51 Posts

November 24th, 2014 08:00

Please don't mix strong rule(i%+j%+k%=100%) and flexible rule(>100%) it is a different. and in you case, it is flexible rule, I suppose it will try to put whole device on EFD, for course it is not possible so the rest will be on FC. So as EMC mentions if case of strong rule you can predict where your data is, but if capacity is not enough you will not able to predict that even if you use srtong (strict) rule.

Right?

419 Posts

January 22nd, 2015 04:00

I see you have marked your own answer as correct here. Probably not the most helpful to others who may check the forum from time to time. 

I suggest you check the following blog http://blog.scummins.com/?p=87 also the FAST VP Technical note available on https://support.emc.com both of these documents provide a good grounding for how FAST VP algorithms work and what the recommended practices you should follow are.

51 Posts

January 22nd, 2015 04:00

Hello!

I've set it is correct cause I gathered all answers in one box to make easy for other people to read it. Do you think it is not good?

419 Posts

January 22nd, 2015 05:00

Hi,

I guess I had trouble understanding the response. I normally award the responder who has been most responsive on the forum. Either way as long as you have the information you need it is the important thing.

51 Posts

January 22nd, 2015 06:00

Please check now Martin, I hope now is clear.

419 Posts

January 23rd, 2015 01:00

Much clearer

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