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 Post subject: Hot Spindles
PostPosted: Thu Mar 07, 2019 11:58 am 

Joined: Wed Jan 16, 2019 4:26 pm
Posts: 6
How do you investigate "hot" (high I/O) spindles when you've already run a tunesys and the chunklets are well-balanced? Is there a way to track this I/O through the LD's in which the drive is participating and on up through the layers?

I'm curious to see if there's one tiny segment of data that's being hammered repeatedly and where these I/O requests are originating.

Edit: some background info, we have two 3PARs, one with six consistently hot spindles, the other with two. I figure whatever host is hammering these blocks might be a good candidate for moving at least part of its data to a pure flash tier. But I need to identify it first.


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 Post subject: Re: Hot Spindles
PostPosted: Thu Mar 07, 2019 1:42 pm 

Joined: Wed Nov 09, 2011 12:01 pm
Posts: 308
tunepd is probably what you want, just use the diagnostic side rather then the move bits to see what is happening.


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 Post subject: Re: Hot Spindles
PostPosted: Fri Mar 08, 2019 4:32 am 

Joined: Mon Sep 21, 2015 2:11 pm
Posts: 784
Location: Europe
I have so many questions and I don't know where to start ....

Something sounds very wrong if you have such clear hot-spots on the physical layer. The 3PAR should distribute data pretty good across multiple LDs crossing multiple PDs when writing to a volume. The only thing that might prevent this is if the data set if very small. In that case it should hit cache and you shouldn't get hammered on the backend.

Alternatively you could have created a CPG and filtered it to only cover 2 or 6 PDs but again, that would be against best practice and just plain stupid.

If this is constant I would try looking at the 3PAR CLI reference guide at the stat commands. statpd you clearly know, statld will point you to which LD is getting hammered, statvv will show which volume and statvlun could point out which server.

srrgiodensity could help you seeing how big the hot data set is.

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