Linux SATA RAID FAQ

Linux SATA RAID FAQ

[Jeff Garzik]

As author of the current Linux SATA driver, I get the brunt of the 
questions and "bug reports" about "Linux doesn't support my hardware 
SATA RAID".  Sigh.  Silly marketing departments.

Thus, I have created a FAQ.  You might sense a theme...

http://www.kernel.org/pub/linux/kernel/people/jgarzik/faq-sata-raid.html

Re: Linux SATA RAID FAQ

[Michael Knigge]

> Thus, I have created a FAQ.  You might sense a theme...
> 
http://www.kernel.org/pub/linux/kernel/people/jgarzik/faq-sata-raid.html


;-) Funny.....

I don't care about RAID, but could you tell which S-ATA 
Controller/Chipset is the best for Hot-Swap?


Thanks,
  Michael

Re: Linux SATA RAID FAQ

[Paul Ionescu]

On Thu, 12 Aug 2004 07:18:10 +0000, Michael Knigge wrote:
> I don't care about RAID, but could you tell which S-ATA 
> Controller/Chipset is the best for Hot-Swap?

Hi Michael,

I think 3ware is the most stable right now, and has his own separate
driver. It is even seen as a SCSI controller by linux, but has SATA or
PATA disks.
Maybe there are some others, but I heard this is stable right now, and
hot-swapping is working on it.

Re: Linux SATA RAID FAQ

[Willy Tarreau]

Hi Jeff,

> http://www.kernel.org/pub/linux/kernel/people/jgarzik/faq-sata-raid.html

I like it. It's fairly simple. I'm always amazed how many people do really
believe that these cards provide hardware RAID !!! The problem is when you
ask a reseller to add a real hardware RAID card in a system you purchase
and you end up with a cheap silicon image... It happened to us once and it's
not funny at all.

Cheers,
Willy

Re: Linux SATA RAID FAQ

[Martin Schlemmer]

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On Thu, 2004-08-12 at 08:33, Jeff Garzik wrote:
> As author of the current Linux SATA driver, I get the brunt of the 
> questions and "bug reports" about "Linux doesn't support my hardware 
> SATA RAID".  Sigh.  Silly marketing departments.
> 
> Thus, I have created a FAQ.  You might sense a theme...
> 
> http://www.kernel.org/pub/linux/kernel/people/jgarzik/faq-sata-raid.html
> 

Would be nice if somebody though could add how to compile dmraid
with make-3.80 :/


-- 
Martin Schlemmer

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Re: Linux SATA RAID FAQ

[J. Ryan Earl]

Willy Tarreau wrote:

>I like it. It's fairly simple. I'm always amazed how many people do really
>believe that these cards provide hardware RAID !!! The problem is when you
>ask a reseller to add a real hardware RAID card in a system you purchase
>and you end up with a cheap silicon image... It happened to us once and it's
>not funny at all.
>
On the brightside, md raid5 is often faster than hardware raid5.  At 
least on the 7000 and 8000 series of 3ware hardware; the 9000 series 
looks promising though.  I haven't seen megaraid SATA numbers, and I 
don't know what happened to the SX8.

When the libata Marvell drivers come out, you'll have a cheap upgrade 
path for PCI-X boards if you want fast md raid: 
http://www.supermicro.com/products/accessories/addon/DAC-SATA-MV8.cfm  
$100 to add 8 unbottlenecked SATA ports to your server motherboard.

-ryan

Re: Linux SATA RAID FAQ

[Alan Cox]

On Sad, 2004-08-14 at 01:31, J. Ryan Earl wrote:
> On the brightside, md raid5 is often faster than hardware raid5.  At 
> least on the 7000 and 8000 series of 3ware hardware; the 9000 series 
> looks promising though.  I haven't seen megaraid SATA numbers, and I 
> don't know what happened to the SX8.

Be cautious what you measure. One of he problems until you reach PCI-X
is PCI bandwidth. Thus software md5 can look good but the moment its
combined with other PCI activity goes down the pan entirely.

> When the libata Marvell drivers come out, you'll have a cheap upgrade 
> path for PCI-X boards if you want fast md raid: 

Agreed. PCI-X will change a lot of this for boxes that are not very
cpu/memory limited.

Re: Linux SATA RAID FAQ

[J. Ryan Earl]

Alan Cox wrote:

>Be cautious what you measure. One of he problems until you reach PCI-X
>is PCI bandwidth. Thus software md5 can look good but the moment its
>combined with other PCI activity goes down the pan entirely.
>  
>
Right, which is why you'd think hardware based RAID would fair better, 
the parity information or mirror'd writes would only require one 
transfer/transaction across the PCI bus.  However, when benchmarking a 
3Ware 4-port ide raid controller (7000) we saw 40-50MB/sec read/write on 
4x160GB drives raid5.  With md raid5 (same controller, HDs, FS, etc)  we 
saw 100MB/sec read, 60MB/sec write.  This was using max 15% CPU on a 
2.4GHz Pentium4, with a 32bit/33MHz PCI bus.

>  
>
>>When the libata Marvell drivers come out, you'll have a cheap upgrade 
>>path for PCI-X boards if you want fast md raid: 
>>    
>>
>
>Agreed. PCI-X will change a lot of this for boxes that are not very
>cpu/memory limited.
>  
>
 From the testing I've done, interconnect bandwidth has always been the 
limiting factor for the md driver.  Using cheap ($~230) PCI-X 
motherboards--http://www.supermicro.com/products/motherboard/P4/E7210/P4SCT+.cfm--with 
dedicated gigE channels, you can make high density/price and 
performance/price NAS type appliances with no bottlenecks.  For <$3K you 
can build a 2TB NAS server that'll keep a 250MB/s gigE link saturated.

-ryan