XP RAID vs md

XP RAID vs md

[Vladimir Milovanovic]

Wow... I hope that one of the maintainers will comment on this, I didn't 
even know that XP had a sw RAID implementation. Up to 100% more on read 
and 60% more on write is quite a significant margin. Is there anything 
in favour of the md driver if this is true?

Re: XP RAID vs md

[Lars Marowsky-Bree]

On 2003-04-02T14:19:46,
   Vladimir Milovanovic <vlad@webmail.co.za> said:

> Wow... I hope that one of the maintainers will comment on this, I didn't 
> even know that XP had a sw RAID implementation. Up to 100% more on read 
> and 60% more on write is quite a significant margin. Is there anything 
> in favour of the md driver if this is true?

I've not really checked these numbers yet, so take the following with a grain
of salt.

However, with RAID1 for example, I got approximately twice the read speed and
95% of the write speed (compared to just using a single disk).

I have a really hard time imagining a 100% read boost; that would simply
exceed disk bandwidth, and 60% writes - how should that work?

I'm not claiming md is perfect or the fastest imaginable solution, but it is
rather close to theoretical disk bandwidth. A two digit percentage performance
improvement just can't be done.



Sincerely,
    Lars Marowsky-Brée <lmb@suse.de>

-- 
SuSE Labs - Research & Development, SuSE Linux AG
  
"If anything can go wrong, it will." "Chance favors the prepared (mind)."
  -- Capt. Edward A. Murphy            -- Louis Pasteur
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Re: XP RAID vs md

[Scott McDermott]

Lars Marowsky-Bree on Wed  2/04 17:27 +0200:
> > Wow... I hope that one of the maintainers will comment
> > on this, I didn't even know that XP had a sw RAID
> > implementation. Up to 100% more on read and 60% more on
> > write is quite a significant margin. Is there anything
> > in favour of the md driver if this is true?
> 
> However, with RAID1 for example, I got approximately twice
> the read speed [...]
> 
> I have a really hard time imagining a 100% read boost;
> that would simply exceed disk bandwidth [...]

isn't "100%" the same as double? If you get "approximately
twice" then you are getting 100% already...

Re: XP RAID vs md

[Illtud Daniel]

[posted & mailed]

Lars Marowsky-Bree wrote:

> > Wow... I hope that one of the maintainers will comment on this, I didn't
> > even know that XP had a sw RAID implementation. Up to 100% more on read
> > and 60% more on write is quite a significant margin. Is there anything
> > in favour of the md driver if this is true?
> 
> I've not really checked these numbers yet, so take the following with a grain
> of salt.

Have a look at http://www.hpl.hp.com/techreports/2002/HPL-2002-352.pdf
- that'll tell you were the figures are from - the 100% is worst-case.
 
> However, with RAID1 for example, I got approximately twice the read speed and
> 95% of the write speed (compared to just using a single disk).

One thing I forgot to mention in my post is that this is all (AFAICS)
RAID0.
 
> I have a really hard time imagining a 100% read boost; that would simply
> exceed disk bandwidth, and 60% writes - how should that work?

The md driver seriously underperforms at certain request sizes, and
is generally underperforming. The average boost is less, but still about
40-60% read and 30-40% write. XP's RAID0 is better than JBOD above a
certain request size, which is pretty good.
 
> I'm not claiming md is perfect or the fastest imaginable solution, but it is
> rather close to theoretical disk bandwidth. A two digit percentage performance
> improvement just can't be done.

Well, that's why I asked in my original post for people to look at
the report. Is isn't that long and it's pretty clear (although short
on config details).

-- 
Illtud Daniel                                 illtud.daniel@llgc.org.uk
Uwch Ddadansoddwr Systemau                       Senior Systems Analyst
Llyfrgell Genedlaethol Cymru                  National Library of Wales
Yn siarad drosof fy hun, nid LlGC   -  Speaking personally, not for NLW

Re: XP RAID vs md

[Vladimir Milovanovic]

Well Daniel what is your take on this? I am very interested in this 
since I am working on a project which has to use RAID, and performance 
is paramount (after reliability of course). I need to make a decision, 
and I would like very much to stick with md, since it is what I know and 
am used to. But if one can get huge performance margins using XP, then I 
am going to have to consider that.

Cheers,

Vlad.


Illtud Daniel wrote:

>[posted & mailed]
>
>Lars Marowsky-Bree wrote:
>
>  
>
>>>Wow... I hope that one of the maintainers will comment on this, I didn't
>>>even know that XP had a sw RAID implementation. Up to 100% more on read
>>>and 60% more on write is quite a significant margin. Is there anything
>>>in favour of the md driver if this is true?
>>>      
>>>
>>I've not really checked these numbers yet, so take the following with a grain
>>of salt.
>>    
>>
>
>Have a look at http://www.hpl.hp.com/techreports/2002/HPL-2002-352.pdf
>- that'll tell you were the figures are from - the 100% is worst-case.
>
>  
>
>>However, with RAID1 for example, I got approximately twice the read speed and
>>95% of the write speed (compared to just using a single disk).
>>    
>>
>
>One thing I forgot to mention in my post is that this is all (AFAICS)
>RAID0.
>
>  
>
>>I have a really hard time imagining a 100% read boost; that would simply
>>exceed disk bandwidth, and 60% writes - how should that work?
>>    
>>
>
>The md driver seriously underperforms at certain request sizes, and
>is generally underperforming. The average boost is less, but still about
>40-60% read and 30-40% write. XP's RAID0 is better than JBOD above a
>certain request size, which is pretty good.
>
>  
>
>>I'm not claiming md is perfect or the fastest imaginable solution, but it is
>>rather close to theoretical disk bandwidth. A two digit percentage performance
>>improvement just can't be done.
>>    
>>
>
>Well, that's why I asked in my original post for people to look at
>the report. Is isn't that long and it's pretty clear (although short
>on config details).
>
>--
>Illtud Daniel                                 illtud.daniel@llgc.org.uk
>Uwch Ddadansoddwr Systemau                       Senior Systems Analyst
>Llyfrgell Genedlaethol Cymru                  National Library of Wales
>Yn siarad drosof fy hun, nid LlGC   -  Speaking personally, not for NLW
>-
>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: XP RAID vs md

[Illtud Daniel]

Vladimir Milovanovic wrote:
 
> Well Daniel what is your take on this? I am very interested in this
> since I am working on a project which has to use RAID, and performance
> is paramount (after reliability of course).

...in which case I'd go for a hardware SCSI solution. The AMI
Megaraid (now LSI?) cards have served me well. You can afford one
by not buying XP...

> I need to make a decision,
> and I would like very much to stick with md, since it is what I know and
> am used to. But if one can get huge performance margins using XP, then I
> am going to have to consider that.

You must remember that this is RAID0, and says nothing about
other RAID levels. I'm assuming you wouldn't be implementing a
RAID0 (not on its own, anyway - maybe 5+0) if you're looking
for reliability. You've also got to look at where you need the
speed - is this a network file server? In which case your
bottleneck is probably the network, unless you've got more than
two gigabit ethernet cards. Tell us more about what your project
needs RAID for, and we can (probably) tell you that md is just
what you need. I'd be very wary of going over to XP on the back
of this one report, since you're opening yourself up to a load
of extra costs (on everything!). If you've got the money, then
why not just go for hardware SCSI RAID?

I've benchmarked NT4.0's RAID0 of two hardware RAID 5 arrays
against linux's (about a year ago) and linux smoked NT, which
is why this report surprised me, I wasn't aware that XP had
come on so far, and I was after some feedback from the md
developers as to whether they could spot another reason for the
results in the report.

-- 
Illtud Daniel                                 illtud.daniel@llgc.org.uk
Uwch Ddadansoddwr Systemau                       Senior Systems Analyst
Llyfrgell Genedlaethol Cymru                  National Library of Wales
Yn siarad drosof fy hun, nid LlGC   -  Speaking personally, not for NLW

RE: XP RAID vs md

[Rechenberg, Andrew]

I'm not sure if this is true on XP, but on Win2K the only software RAID available is 0, 1, and 5.  You cannot combine already-created software RAID devices to create RAID10, or RAID50 arrays for instance.  This type of array is very easy with Linux software RAID.

So if all that you want is simple arrays, XP would be fine, but for database servers that need both redundancy and performance, XP software RAID would probably not work for you.

My 2¢
Andy.

> -----Original Message-----
> From: Vladimir Milovanovic [mailto:vlad@webmail.co.za] 
> Sent: Wednesday, April 02, 2003 7:20 AM
> To: raid-list
> Subject: XP RAID vs md
> 
> 
> Wow... I hope that one of the maintainers will comment on 
> this, I didn't 
> even know that XP had a sw RAID implementation. Up to 100% 
> more on read 
> and 60% more on write is quite a significant margin. Is there 
> anything 
> in favour of the md driver if this is true?
> 
> 
> 
> 
> -
> 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
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