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-   -   hardware raid reliability? (http://www.linux-archive.org/gentoo-embedded/179533-hardware-raid-reliability.html)

Ned Ludd 10-20-2008 04:47 PM

hardware raid reliability?
 
On Mon, 2008-10-20 at 19:10 +0300, Jan Klod wrote:
> Hello.
>
> Which option is safer in general, when talking about small embedded boards:
> hardware or software raid1?

To be honest. I don't think I've ever heard anybody mention RAID at any
level with respects to embedded anything. Most embedded devices are on
FLASH. Unless it was a RAID controller itself itself that is embedded.


--
Ned Ludd <solar@gentoo.org>
Gentoo Linux

Janusz Syrytczyk 10-20-2008 08:02 PM

hardware raid reliability?
 
Monday 20 October 2008 18:10:20 Jan Klod napisaƂ(a):
> Hello.
>
> Which option is safer in general, when talking about small embedded boards:
> hardware or software raid1?

If you're paranoid ;-) you could use linux mirror on 2 (or more, for the more
paranoid ;-) ) storage devices.

When you do raid you should conduct some extreme tests: disconnect on heavy
load, burn one of your CFs with lighter, etc. to prove yourself that it is
worth of the extra job you do (well I do raid everything I have of servers,
it makes me sleep better, but once I had a raid and...)

If I'd have to create some extremely durable storage I would use the simplest
solution, so its linux raid. But it is generally safe to leave all on ro
partition with hardcoded default configuration (or steps for acquiring this
configuration) and make the rest as small as it could be.

Oh, but that was general anyway.

Janusz.

wireless 10-20-2008 11:04 PM

hardware raid reliability?
 
Jan Klod wrote:

> Which option is safer in general, when talking about small embedded boards:
> hardware or software raid1?

Since most embedded system utilize a much larger percentage of
hardware resources, software based raid on an embedded system could
cause too much hardware resource (cpu cycles, memory etc) to be
used, depending on the specifics of your board. If you can put
a hardware raid chip on the board, and you *really* need raid,
then that would be better.

cost constraints are another dimension of your chip selection process.


All of this 'begs' the question what do you really mean by 'safer"?


hth,
James

"Geoff Swan" 10-20-2008 11:12 PM

hardware raid reliability?
 
> Which option is safer in general, when talking about small embedded
boards:
> hardware or software raid1?

In terms of recovering data after a crash I think software raid is
safer, or
at least easier to recover. The advantage being that the data storage on
a software
RAID1 disk looks like any other non-raid disk. Depending on the hardware
RAID controller
you may not be able to read the data on your disk without the hardware
raid controller.

Geoff

- I think I think, therefore I possibly am -

"Jan Klod" 10-25-2008 08:19 PM

hardware raid reliability?
 
Ah, I nearly forgot this post!

Two boards? Synchronisation mechanism? (just interested)
Anyway, would be too expensive for too little gain. Not that paranoid
at the moment, sorry :)

Well, I already came to my conclusions about how should I do, just
details is quite uncertain.
Since that is not really a "hardware raid1" on my board (C7 CPU) and
there are lot more issues, if controller burns, I put ideas about
hardware raid away quite soon.
Linux software raid? Could be, but it still holds the risk of "what
happens if disk controllers write crap somehow"? (yes, yes, unlikely,
but still)

Since raid1 would be nearly two times slower for C7 board and I mostly
do not need immediate synchronisation (plus power consumption is very
limited), I figured out something interesting; at least for me: system
is mostly operating single disk, but periodically synchronises*
contents with second disk, that is not spinning in other times. For
extra safety, it would be very good, if there was moving backup in
RAM, which mirrors files matching paths in list. By "moving" I
understand filling some 500MB with those important data copies and
deleting oldest, that would be synchronised to second HDD, if used
properly.

* that should be done by maintaining changelog of filesystem since
last sync for all files - any suggestions how to do that?

And .. doest that seam an overkill, if I want that RAM mirror work
well and "move"?

Jan

On 10/21/08, Geoff Swan <geoff.swan@compucat.com> wrote:
>
>> Which option is safer in general, when talking about small embedded
> boards:
>> hardware or software raid1?
>
> In terms of recovering data after a crash I think software raid is
> safer, or
> at least easier to recover. The advantage being that the data storage on
> a software
> RAID1 disk looks like any other non-raid disk. Depending on the hardware
> RAID controller
> you may not be able to read the data on your disk without the hardware
> raid controller.
>
> Geoff
>
> - I think I think, therefore I possibly am -
>
>

Mike Frysinger 10-26-2008 07:01 AM

hardware raid reliability?
 
On Monday 20 October 2008, Jan Klod wrote:
> Which option is safer in general, when talking about small embedded boards:
> hardware or software raid1?

in general, linux software raid tends to be more robust/dependable than
hardware solutions. it certainly gets a lot more testing. and depending on
the hardware implementation, performance may be better.

but ive never heard of people doing embedded systems and raid ... the two
areas simply dont intersect ...
-mike


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