Culprit...

classic Classic list List threaded Threaded
4 messages Options
Reply | Threaded
Open this post in threaded view
|

Culprit...

Carl Howell
I've got an aggregate on a FAS2554c, running ONTAP 9, that runs at over 4500 read IOPS constantly. All of the volumes in the aggregate don't generate near that many IOPS and SnapMirror doesn't look like the cause either. I've used OCUM, statistics show...., etc, and haven't been able to find out what's causing this. Any suggestions?

Thanks,

--Carl

_______________________________________________
Toasters mailing list
[hidden email]
http://www.teaparty.net/mailman/listinfo/toasters
Reply | Threaded
Open this post in threaded view
|

Re: Culprit...

Edward Rolison
Try 'priv set -q diag; wafl scan status'. You may find it's a deswizzle operation if it's a snap mirror destination. 

On 18 October 2016 at 20:13, Carl Howell <[hidden email]> wrote:
I've got an aggregate on a FAS2554c, running ONTAP 9, that runs at over 4500 read IOPS constantly. All of the volumes in the aggregate don't generate near that many IOPS and SnapMirror doesn't look like the cause either. I've used OCUM, statistics show...., etc, and haven't been able to find out what's causing this. Any suggestions?

Thanks,

--Carl

_______________________________________________
Toasters mailing list
[hidden email]
http://www.teaparty.net/mailman/listinfo/toasters



_______________________________________________
Toasters mailing list
[hidden email]
http://www.teaparty.net/mailman/listinfo/toasters
Reply | Threaded
Open this post in threaded view
|

Re: Culprit...

Flores, Paul

 

 

does seem to be running away with the box.  Was this box upgraded from an older version of software?

 

From: <[hidden email]> on behalf of Edward Rolison <[hidden email]>
Date: Wednesday, October 19, 2016 at 3:00 AM
To: "NGC-chowell-uwf.edu" <[hidden email]>
Cc: "[hidden email]" <[hidden email]>
Subject: Re: Culprit...

 

Try 'priv set -q diag; wafl scan status'. You may find it's a deswizzle operation if it's a snap mirror destination. 

 

On 18 October 2016 at 20:13, Carl Howell <[hidden email]> wrote:

I've got an aggregate on a FAS2554c, running ONTAP 9, that runs at over 4500 read IOPS constantly. All of the volumes in the aggregate don't generate near that many IOPS and SnapMirror doesn't look like the cause either. I've used OCUM, statistics show...., etc, and haven't been able to find out what's causing this. Any suggestions?

 

Thanks,

 

--Carl


_______________________________________________
Toasters mailing list
[hidden email]
http://www.teaparty.net/mailman/listinfo/toasters

 


_______________________________________________
Toasters mailing list
[hidden email]
http://www.teaparty.net/mailman/listinfo/toasters
Reply | Threaded
Open this post in threaded view
|

Re: Culprit...

Michael Bergman
On 2016-10-19 17:35, Flores, Paul wrote:
> does seem to be running away with the box. Was this box upgraded from an
> older version of software?

Do you use .snapshot/ for a lot on this box..? I.e. do you read from them,
more than like now and then (for occasional restores)?

You can [manually] kill any BG deswizzler scanner whenever you like, it
won't do any harm to anything.

BG deswizzling isn't terribly important to run in majority of scenarios.
The deswizzler scanner is quite stupid (inefficient), it reads 4K WAFL
blocks and it traverses inodes.

If you have dense file data, it takes forever to run, for no benefit
basically. Especially in a larger FAS (which this isn't, I know) deswizzling
can (should IMO!) simply be turned off.  There's a *global* knob that does
this, in 7-mode it looks like this:

wafl.deswizzle.enable        off

Don't know off the top of my head for cDOT, sorry.
N.B. deswizzling will still happen, on the fly, when WAFL blocks are read
the first time and there's an extra pointer there which can be taken away.

Anyone who has ever done reallocate start -A -o <aggr_name> on a large Aggr
with FlexVols of very high inode density, have been in contact with the BG
deswizzler scanners.... they hurt the system, pretty much for nothing.  As
soon as the blkrealloc phase has finished, and one BG scanner per FlexVol is
kicked off *all at once*.

I ALWAYS just kill all of those, pronto. By doing reallocate stop quite
simply the minute the blkrealloc phase is finished.

Hope this helps!

/M

> *From: *<[hidden email]> on behalf of Edward Rolison
> <[hidden email]>
> *Date: *Wednesday, October 19, 2016 at 3:00 AM
> *To: *"NGC-chowell-uwf.edu" <[hidden email]>
> *Cc: *"[hidden email]" <[hidden email]>
> *Subject: *Re: Culprit...
>
> Try 'priv set -q diag; wafl scan status'. You may find it's a deswizzle
> operation if it's a snap mirror destination.
>
> On 18 October 2016 at 20:13, Carl Howell <[hidden email]
> <mailto:[hidden email]>> wrote:
>
>     I've got an aggregate on a FAS2554c, running ONTAP 9, that runs at over
>     4500 read IOPS constantly. All of the volumes in the aggregate don't
>     generate near that many IOPS and SnapMirror doesn't look like the cause
>     either. I've used OCUM, statistics show...., etc, and haven't been able
>     to find out what's causing this. Any suggestions?
>
>     Thanks,
>
>     --Carl
_______________________________________________
Toasters mailing list
[hidden email]
http://www.teaparty.net/mailman/listinfo/toasters