Technically, doing any of this (mixing drive speeds in RGs or drive
sizes in RGs) will work just fine. The only issue is the potential of
performance degradation in the future once\if the system is under
stress.
The drives spinning slowest will take the longest to have writes flushed
to them - thusly forcing the CP to take longer and impacting the entire
system. This is true within RGs or across multiple RGs in an aggregate.
Heck, this is true even if you have multiple aggregates and one is
comprised of slower disks than the others (or is slow due to other
reasons such as workload, fragmentation, etc) - a write (CP) is a GLOBAL
ENTITY and it is atomic in nature: if you have data in a CP for
multiple RGs\TradVols\Aggrs and one takes forever to flush to disk, then
the WHOLE CP takes forever.
That said, all of this 'chicken little\sky falling' stuff is just
conjecture. On a lightly loaded system, you'll never see issues. Only
under stress will all of this stuff bubble to the surface.
Oh - and FWIW, if you write data in a less-than optimal fashion, then
subsequent reads will have the same issues (higher latencies),
potentially causing performance problems.
Remember - all of this could still take place and you could potentially
never see the effects depending on the circumstances and how the
applications handles increased latencies.
I hope all of that is clearly written?
Glenn
-----Original Message-----
From: maclean(a)cs.mcgill.ca [mailto:maclean@cs.mcgill.ca]
Sent: Thursday, September 21, 2006 2:41 PM
To: Glenn Walker
Cc: toasters(a)mathworks.com
Subject: RE: Mixed disk sizes within a single aggregate
I always thought you would have problems mixing speeds in a
raid group. Specifically you would see 'failing servo motor'
autosupport messages.
Or are you suggesting raid groups segregated by speed and
only mixing speeds within an aggregate made up of the
speed based raid groups?
-Matthew
On Thu, September 21, 2006 11:01 am, Glenn Walker wrote:
> Exactly :)
>
>
> Consistency is key: always try to keep same disk sizes speeds in
> aggregates. I'd feel more comfortable adding disks with faster speeds
> than larger sizes - there will be no future performance degradation
from
> this.
>
> Glenn
>
>
>
> -----Original Message-----
> From: Crawford, Mark (CBC) [mailto:Mark.Crawford@CapBlueCross.COM]
> Sent: Thu 9/21/2006 10:53 AM
> To: David Knight; Glenn Walker
> Cc: Paul.Brosseau(a)netapp.com; jeff.mery(a)ni.com; toasters(a)mathworks.com
> Subject: RE: Mixed disk sizes within a single aggregate
>
>
> When the stripes fill the equivalent of the smaller disks, wafl will
> start striping only on the larger disks. This will cause performance
> degradation due to "hot" disks.
>
> -----Original Message-----
> From: owner-toasters(a)mathworks.com
[mailto:owner-toasters@mathworks.com]
> On Behalf Of David Knight
> Sent: Thursday, September 21, 2006 9:44 AM
> To: ggwalker(a)mindspring.com
> Cc: Paul.Brosseau(a)netapp.com; jeff.mery(a)ni.com; toasters(a)mathworks.com
> Subject: Re: Mixed disk sizes within a single aggregate
>
>
> I think wafl stripes across all disks in an aggregate.
> I'm not sure how it respond to having one raid group with larger disks
-
> likely it will not use part of them. I'm pretty sure netapp recommends
all
> disks in an aggregate be the same size, or, it will assume they are
all
> the size of the smallest disk. Of course, I could be wrong . . .
>
>
> David
>
>
>> Remember that WAFL still writes across the entire aggregate. Having
a
>>
>
>> slower RAID group in an aggregate of faster raid groups would be akin
to
>> having a slower disk in a RG of faster disks, would it not?
>>
>>
>>
>> Glenn
>>
>>
>>
>>
>> ________________________________
>>
>>
>> From: owner-toasters(a)mathworks.com
>> [mailto:owner-toasters@mathworks.com]
>> On Behalf Of Brosseau, Paul
>> Sent: Wednesday, September 20, 2006 8:05 PM
>> To: Jeff Mery; toasters(a)mathworks.com
>> Subject: RE: Mixed disk sizes within a single aggregate
>>
>>
>>
>>
>> Mixing disk sizes in an aggregate is not a problem as long as you
>> create RAID groups for each kind of disk. WAFL creates stripes at
the
>
>> RAID group level. For best results create complete RAID groups each
>> time you add disks to an aggregate.
>>
>>
>>
>> Paulb
>>
>>
>>
>>
>> ________________________________
>>
>>
>> From: Jeff Mery [mailto:jeff.mery@ni.com]
>> Sent: Wednesday, September 20, 2006 3:30 PM
>> To: toasters(a)mathworks.com
>> Subject: Mixed disk sizes within a single aggregate
>>
>>
>>
>> Greetings fellow toasters!
>> <Background>
>> We're looking at moving our 2 FAS940 systems from tradtional volumes
>> to flexvols + aggregates. </Background>
>>
>>
>> It would seem to me that the same rules and guidelines for creating
>> traditional volumes now apply directly to the aggregate level (for
the
>
>> most part). By rules and guidelines I mean things like trying not to
>> mix disk sizes, try to avoid volumes (now aggregates?) that span FC
>> adapters, etc.
>>
>> Are any of these things still a concern on modern versions of ONTAP
>> (7+)? Does anyone have any best practices they'd be willing to share
>> in regards to aggregate creation? NOW says "make them as big as
possible
>> using as many spindles as possible", but that doesn't really
> help much.
>> We use our filers for unstructured data only; cifs + nfs but no
>> databases, no snapmirror, no snapvault, etc..
>>
>> TIA,
>> Jeff Mery - MCSE, MCP
>> National Instruments
>>
>>
>>
----------------------------------------------------------------------
>> --
>> -
>> "Allow me to extol the virtues of the Net Fairy, and of all the
>> fantastic dorks that make the nice packets go from here to there.
Amen."
>> TB - Penny Arcade
>>
----------------------------------------------------------------------
>> --
>> -
>>
>>
>
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