HPE EVA Storage

Forced Unit Access on EVAs

 
Patti T
Advisor

Forced Unit Access on EVAs

If SQL sets the FUA bit, requesting that data must reach stable media before the I/O is complete, will the EVA return I/O complete when it reaches cache or will it be forced to do a "write through" and data must be written to disk before the I/O is complete?

Thanks!
7 REPLIES 7
Al Oliveira
New Member

Re: Forced Unit Access on EVAs

the EVA will honor the FUA and so will treat it as write through
Rampy(Venu)
Frequent Advisor

Re: Forced Unit Access on EVAs

When master and slave controller battery is good all disks write back on both master and slave controller's.

master will always do write back no matter what is the status of the slave controller battery.

There are many situations in which master controller battery is bad and slave is good in those cases it handles them differently and it's confidential.
Uwe Zessin
Honored Contributor

Re: Forced Unit Access on EVAs

Is that a verbose way of saying that the EVA does ignore FUA?
;-)
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Rampy(Venu)
Frequent Advisor

Re: Forced Unit Access on EVAs

It might not ignore the FUA.EVA gives confirmation that the data is written once it receives to the cache.It reached the stable media and i/o is marked complete..

EVA works the way i pasted above.i might not know about FUA much.

Your thoughts please...
Patrick Terlisten
Honored Contributor

Re: Forced Unit Access on EVAs

Hi,

let assume that mirrored cache is a "stable media". ;) AFAIK is a IO marked as written if it reaches the cache of the EVA, but only if write-back is actived on a Vdisk. If write-through is set, IO is marked as done if it's written to disk. Can someone confirm this?

Best regards,
Patrick
Best regards,
Patrick
Uwe Zessin
Honored Contributor

Re: Forced Unit Access on EVAs

> EVA gives confirmation that the data is written once it receives to the cache.

Then it ignores it.

> It reached the stable media and i/o is marked complete..

I don't think the EVA cant give two confirmations. Either when the data is in cache (write-back) -or- when the data is stored on physical disk (write-through/FUA).

> EVA works the way i pasted above.

No offense, but the question was about FUA - not how bad batteries change the default caching behavior.

And I think you meant virtual disk owning/non-owning controllers, not the cell master/slave, don't you?



My _guess_ is that the EVA (like several arrays) does ignore FUA to improve performance, because the data is protected by mirrored battery-backed cache memory.
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Rampy(Venu)
Frequent Advisor

Re: Forced Unit Access on EVAs

Yes I agree my mistake..Completely different answer.My Bad.I take it back.
Thanks buddy.