Does software RAID take advantage of SMP, or 64 bit CPU(s)?

Does software RAID take advantage of SMP, or 64 bit CPU(s)?

[Adam Talbot]

A few simple questions about the 2.6.16+ kernel and software RAID.
Does software RAID in the 2.6.16 kernel take advantage of SMP?
Does software RAID take advantage of 64-bit CPU(s)?
If there are any good web sites that cover this information, a link
would be GREAT!

-Adam Talbot

Re: Does software RAID take advantage of SMP, or 64 bit CPU(s)?

[Neil Brown]

On Monday May 22, talbotx@comcast.net wrote:
> A few simple questions about the 2.6.16+ kernel and software RAID.
> Does software RAID in the 2.6.16 kernel take advantage of SMP?

Not exactly.  RAID5/6 tends to use just one cpu for parity
calculations, but that frees up other cpus for doing other important
work.

> Does software RAID take advantage of 64-bit CPU(s)?

No more or less that other code in the kernel.  Sometimes using a 64-bit
CPU is a cost because more data is shuffled around...

Was there some particular sort of 'advantage' that you were thinking
of?

NeilBrown


> If there are any good web sites that cover this information, a link
> would be GREAT!
> 
> -Adam Talbot
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Does software RAID take advantage of SMP, or 64 bit CPU(s)?

[Adam Talbot]

-Neil
I was not looking for any direct advantage.  It is more a money VS
performance thing.  I have a old dual proc Opteron motherboard.  I am
going with 64-bit, but it is much cheaper if I just go buy a nice single
proc board instead of buying two Opterons for my dual proc board.  If I
could get a 1.5~2X performance improvement with SMP I would pay the
extra money.  If there is no major performance difference, I will take
the cheap road.

Thank you for the good input.
-Adam

P.S.  Here is my current plan.
RAID 6, 6X 400GB SATA 2.0 HDD's, Athlon FX 53, 1GB DDR 400, Nvidia based
motherboard, Gb Ethernet.  Storing 15,000+ MP3's, 500+ movies.

Neil Brown wrote:
> On Monday May 22, talbotx@comcast.net wrote:
>   
>> A few simple questions about the 2.6.16+ kernel and software RAID.
>> Does software RAID in the 2.6.16 kernel take advantage of SMP?
>>     
>
> Not exactly.  RAID5/6 tends to use just one cpu for parity
> calculations, but that frees up other cpus for doing other important
> work.
>
>   
>> Does software RAID take advantage of 64-bit CPU(s)?
>>     
>
> No more or less that other code in the kernel.  Sometimes using a 64-bit
> CPU is a cost because more data is shuffled around...
>
> Was there some particular sort of 'advantage' that you were thinking
> of?
>
> NeilBrown
>
>
>   
>> If there are any good web sites that cover this information, a link
>> would be GREAT!
>>
>> -Adam Talbot
>>
>> -
>> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>     
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>   

Re: Does software RAID take advantage of SMP, or 64 bit CPU(s)?

[Nix]

On 23 May 2006, Neil Brown noted:
> On Monday May 22, talbotx@comcast.net wrote:
>> A few simple questions about the 2.6.16+ kernel and software RAID.
>> Does software RAID in the 2.6.16 kernel take advantage of SMP?
> 
> Not exactly.  RAID5/6 tends to use just one cpu for parity
> calculations, but that frees up other cpus for doing other important
> work.

To expand on this, that depends on how many RAID arrays you've got,
since there's one parity-computation daemon per array.

If you have several arrays and are writing to them at the same time,
or several arrays and some are degraded, then several md*_raid*
daemons might be working at once.

But that's not very likely, I'd guess. (I have multiple RAID-5 arrays,
but that's only because I'm trying to get useful RAIDing on multiple
disks of drastically different size.)

-- 
`On a scale of 1-10, X's "brokenness rating" is 1.1, but that's only
 because bringing Windows into the picture rescaled "brokenness" by
 a factor of 10.' --- Peter da Silva