Re: md RAID with enterprise-class SATA or SAS drives

[David Brown <david.brown@hesbynett.no>]

On 11/05/2012 00:49, Roberto Spadim wrote:
> i have dell servers and  i use raid1 in every servers just raid10 or
> raid0 are in hardware because hotswap with hardware is easier to
> implement, but if mdraid could do the job, i don´t see why use hardware
> raid devices (just if they have batery)
>

I think for simple situations, such as just wanting a straight mirror of 
two disks, then hardware raid provided by the supplier is often a good 
choice.  As you say, it can make hotswap easier - you get things like 
little red and green lights on the disk drives.  And the vendor supports 
it and knows how it works.  Also if you've got a more serious hardware 
with BBWC or similar features, then these features may be the deciding 
points.

But there is no doubt that md raid is a lot more flexible than any other 
raid system, it is often faster (especially for smaller setups - 
raid10,far being a prime example), and the money you save on raid cards 
can be spent on extra disks, UPS, etc.

One thing that may be an advantage either way is ease of configuration, 
monitoring, maintenance, and transfer of disks between systems.  With md 
raid, you have a consistent system that is independent of the hardware 
and setup, while every hardware raid system has its own proprietary 
tools, setup, hardware, monitoring software, etc.  So this is often a 
win for md raid - but if you support several hardware raid arrays, and 
use the same vendor for them all, then you have a consistent system 
there too.



> 2012/5/10 David Brown <david.brown@hesbynett.no
> <mailto:david.brown@hesbynett.no>>
>
>     On 10/05/12 23:15, Stan Hoeppner wrote:
>
>         On 5/10/2012 8:51 AM, Phil Turmel wrote:
>
>             Hardware RAID cards usually offer battery-backed write
>             cache, which is
>             very valuable in some applications.  I don't have a need for
>             that kind
>             of performance, so I can't speak to the details.  (Is Stan H.
>             listening?)
>
>
>         Yes, I'm here to drop the hammer, and start a flame war. ;)
>           I've been
>         lurking and trying to stay out of the fray, but you "keep
>         dragging me
>         back in!" --Michael Corleone
>
>         I find the mere existence of this thread a bit comical, as with all
>         others that have preceded it.  I made the comment on this list quite
>         some time ago that md raid is mostly used by hobbyists, and took
>         a lot
>         of heat for that.  The existence of this thread adds ammunition
>         to that
>         argument.
>
>
>     I think you've got that a bit backwards.  Most hobbyists (or
>     low-budget users) who use raid other than motherboard fakeraid will
>     choose Linux md raid.  It may well be that most users of md raid
>     /are/ hobby or low-budget users.  But your implication - that
>     professionals don't use md raid - is completely wrong.
>
>     It's more likely that it is hobby users that discuss these sorts of
>     things - professionals just pay the money that the server
>     manufacturer asks for its supported disks, since paying that is
>     cheaper than spending time discussing things.  I know I mostly
>     follow lists like this in my free time (as a hobbiest) rather than
>     in work time (as a professional).
>
>
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>
>
>
> --
> Roberto Spadim
> Spadim Technology / SPAEmpresarial

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