Hardware RAID vs. Software RAID

Hardware RAID vs. Software RAID

Post by Dave » Wed, 07 May 1997 04:00:00



I've frequently heart the terms "hardware RAID" and "software RAID"
bantered about this and other newsgroups. I'm confused.

Any RAID solution requires both hardware (a SCSI controller -- either
embedded in the system board or an adapter board) and software (either as
part of the OS or using some utility), don't they?

What's your understanding of these two terms?

Thanks.

Enjoy,
Dave
--
Dave Carpenter                    
InterMedia Research Consultants
Specializing in the evaluation of information delivery methodologies

 
 
 

Hardware RAID vs. Software RAID

Post by Malcolm We » Wed, 07 May 1997 04:00:00



>I've frequently heart the terms "hardware RAID" and "software RAID"
>bantered about this and other newsgroups. I'm confused.

>Any RAID solution requires both hardware (a SCSI controller -- either
>embedded in the system board or an adapter board) and software (either as
>part of the OS or using some utility), don't they?

>What's your understanding of these two terms?

Umm... a disk drive contains software, but we still call it a hardware
device.  Thus a hardware RAID product is a thing, consisting of
hardware and the necessary software (firmware) to make it work.

A "pure" hardware RAID product will appear to the host as nothing more
* than a big reliable disk; a software RAID solution is a
technique whereby the host's OS manipulates several disks in concert.

Hardware RAIDs may have a utility interface from the host (for
configuration, etc.), but they don't have to have one -- interaction
may be performed via a front panel, or some such.

Quote:>Dave Carpenter                    

Malc.

 
 
 

Hardware RAID vs. Software RAID

Post by David K. Spence » Wed, 07 May 1997 04:00:00




: I've frequently heart the terms "hardware RAID" and "software RAID"
: bantered about this and other newsgroups. I'm confused.
:
: Any RAID solution requires both hardware (a SCSI controller -- either
: embedded in the system board or an adapter board) and software (either as
: part of the OS or using some utility), don't they?

Well, yes--at some level there is always "Array Management Software"
that makes the operating system think that multiple physical disks
are to be treated as one virtual logical disk.  This is the software
which handles algorithms for things like maintaining data integrity
if a disk goes away, for handling caches, etc.  This is not to be
confused with the software which allows users to monitor and
configure their RAID units, like through a GUI which notifies
the user of faults on disks, etc.  The software that's being
discussed here is the software which handles shuffling around
checksums, and that sort of activity.

However, the question is where that software lives.  In "hardware RAID"
the software lives on a controller card, usually inside the disk
array cabinet itself, though placing that controller card inside a
host is also a possibility. In "software RAID" the software runs
on the host computer.

The "RAID Advisory Board" calls "hardware RAID" a "subsystem-based
disk array," meaning that the software executes in the array's
controller card.  The benefit of this type of array is that since it
generally uses SCSI buses to connect to the host, it can be connected
to a number of different types of hosts without needing to port
the RAID software.  It is also the case that since the software runs
on the controller card, it doesn't have any impact on computing speed
on the host.  

The RAB calls "software RAID" "host-based disk arrays."  This type of
array also has advantages--one of which is that by distributing the
software and disks over multiple hosts you can give the system higher
availability.  They are cheaper, and often more easily configurable.
However, they are usually less powerful and slower, since the software
usually has less low-level commands available to it with which to control
the disks.

I hope I wasn't just repeating a bunch of stuff you already knew...
most of this information came more or less verbatim from the
RAID Advisory Board's publication "The RAIDBook," published in
June of 1993.

-David Spencer, Software Engineer, CLARiiON Advanced Storage Solutions

 
 
 

Hardware RAID vs. Software RAID

Post by Dave » Thu, 08 May 1997 04:00:00


David:
Thanks for clearing up the definitions.

It seems that the difference is that software RAID solutions live on the
host system, regardless whether or not a host SCSI controller is
installed. A hardware RAID solution is one that is transparent to the host
system. The hardware solution connects to the host via a single SCSI cable
and has the controller and several disks (not necessarily SCSI flavors) in
a stand-alone cabinet.

The mud is now clearer.

Thanks.

Enjoy,
Dave

=====

Quote:>   Well, yes--at some level there is always "Array Management Software"
>   that makes the operating system think that multiple physical disks
>   are to be treated as one virtual logical disk.  This is the software
>   which handles algorithms for things like maintaining data integrity
>   if a disk goes away, for handling caches, etc.  This is not to be
>   confused with the software which allows users to monitor and
>   configure their RAID units, like through a GUI which notifies
>   the user of faults on disks, etc.  The software that's being
>   discussed here is the software which handles shuffling around
>   checksums, and that sort of activity.

>   However, the question is where that software lives.  In "hardware RAID"
>   the software lives on a controller card, usually inside the disk
>   array cabinet itself, though placing that controller card inside a
>   host is also a possibility. In "software RAID" the software runs
>   on the host computer.

>   The "RAID Advisory Board" calls "hardware RAID" a "subsystem-based
>   disk array," meaning that the software executes in the array's
>   controller card.  The benefit of this type of array is that since it
>   generally uses SCSI buses to connect to the host, it can be connected
>   to a number of different types of hosts without needing to port
>   the RAID software.  It is also the case that since the software runs
>   on the controller card, it doesn't have any impact on computing speed
>   on the host.  

>   The RAB calls "software RAID" "host-based disk arrays."  This type of
>   array also has advantages--one of which is that by distributing the
>   software and disks over multiple hosts you can give the system higher
>   availability.  They are cheaper, and often more easily configurable.
>   However, they are usually less powerful and slower, since the software
>   usually has less low-level commands available to it with which to control
>   the disks.

>   I hope I wasn't just repeating a bunch of stuff you already knew...
>   most of this information came more or less verbatim from the
>   RAID Advisory Board's publication "The RAIDBook," published in
>   June of 1993.

>   -David Spencer, Software Engineer, CLARiiON Advanced Storage Solutions

Enjoy,
Dave
--
Dave Carpenter                    
InterMedia Research Consultants
Specializing in the evaluation of information delivery methodologies
 
 
 

Hardware RAID vs. Software RAID

Post by tskel... » Thu, 08 May 1997 04:00:00



enlightened us with the following masterfully crafted prose:

Quote:>David:
>Thanks for clearing up the definitions.

>It seems that the difference is that software RAID solutions live on the
>host system, regardless whether or not a host SCSI controller is
>installed. A hardware RAID solution is one that is transparent to the host
>system. The hardware solution connects to the host via a single SCSI cable
>and has the controller and several disks (not necessarily SCSI flavors) in
>a stand-alone cabinet.

>The mud is now clearer.

>Thanks.

>Enjoy,
>Dave

Not exactly, Dave - hardware RAID does not require an external chassis
at all. There are many SCSI RAID adapters that are simply internal
cards that connect to internal drives.

Visit www.adaptec.com - your SCSI RAID questions will be answered.

- Show quoted text -

Quote:>=====

>>   Well, yes--at some level there is always "Array Management Software"
>>   that makes the operating system think that multiple physical disks
>>   are to be treated as one virtual logical disk.  This is the software
>>   which handles algorithms for things like maintaining data integrity
>>   if a disk goes away, for handling caches, etc.  This is not to be
>>   confused with the software which allows users to monitor and
>>   configure their RAID units, like through a GUI which notifies
>>   the user of faults on disks, etc.  The software that's being
>>   discussed here is the software which handles shuffling around
>>   checksums, and that sort of activity.

>>   However, the question is where that software lives.  In "hardware RAID"
>>   the software lives on a controller card, usually inside the disk
>>   array cabinet itself, though placing that controller card inside a
>>   host is also a possibility. In "software RAID" the software runs
>>   on the host computer.

>>   The "RAID Advisory Board" calls "hardware RAID" a "subsystem-based
>>   disk array," meaning that the software executes in the array's
>>   controller card.  The benefit of this type of array is that since it
>>   generally uses SCSI buses to connect to the host, it can be connected
>>   to a number of different types of hosts without needing to port
>>   the RAID software.  It is also the case that since the software runs
>>   on the controller card, it doesn't have any impact on computing speed
>>   on the host.  

>>   The RAB calls "software RAID" "host-based disk arrays."  This type of
>>   array also has advantages--one of which is that by distributing the
>>   software and disks over multiple hosts you can give the system higher
>>   availability.  They are cheaper, and often more easily configurable.
>>   However, they are usually less powerful and slower, since the software
>>   usually has less low-level commands available to it with which to control
>>   the disks.

>>   I hope I wasn't just repeating a bunch of stuff you already knew...
>>   most of this information came more or less verbatim from the
>>   RAID Advisory Board's publication "The RAIDBook," published in
>>   June of 1993.

>>   -David Spencer, Software Engineer, CLARiiON Advanced Storage Solutions

>Enjoy,
>Dave
>--
>Dave Carpenter                    
>InterMedia Research Consultants
>Specializing in the evaluation of information delivery methodologies

================
TSkel


(remove "removethis" from e-mail address - anti-spam tactic)

 
 
 

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I am looking at putting a raid system in and am getting conflicting stories. We
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Which is better hardware or software?

Thanks
Randy

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