Data integritty in RAID5?

[Jose]

Hi All,

With all HDDs working, does RAID5 have any advantage as far as data
integrity is concerned - as when files are being read/written,?

Assume, that in 1 hdd, a portion of a file has become corrupted. While
reading that file, will the system parity, or error correction, or
something else, to detected that, and repair the file?

Thanks,
Jose

 

[Arno Wagner]

Hi All,

With all HDDs working, does RAID5 have any advantage as far as data
integrity is concerned - as when files are being read/written,?

Assume, that in 1 hdd, a portion of a file has become corrupted. While
reading that file, will the system parity, or error correction, or
something else, to detected that, and repair the file?

Depends on the corruption.

Arno

 

[Odie Ferrous]

Hi All,

With all HDDs working, does RAID5 have any advantage as far as data
integrity is concerned - as when files are being read/written,?

Assume, that in 1 hdd, a portion of a file has become corrupted. While
reading that file, will the system parity, or error correction, or
something else, to detected that, and repair the file?

Thanks,
Jose

RAID has no way of knowing a file is corrupt, unless the file becomes
corrupt due to failure of the raid or bad sectors on the hard drives,
etc, in which case you might get some sort of error message depending on
your raid / controller setup.

RAID works in bits and bytes - not on file formats / signatures /
structures. It doesn't know whether you're working with a jpg or a doc,
so won't know if an already-corrupt file is worked with.


Duncan

 

[Jose]

RAID has no way of knowing a file is corrupt, unless the file becomes
corrupt due to failure of the raid or bad sectors on the hard drives,
etc, in which case you might get some sort of error message depending on
your raid / controller setup.

Well, since it stores, parity information, I thought it might/could
use that while reading files to check for their integrity - I know it
would delay the process.

If it would recover, fix, or move the data on bad sectors, that's
something nice, already.

I suppose we're still talking about RAID5 - which is what I originally
asked about - not RAID 1 (or does RAID1 also handle bad sectors
automatically?)

Thanks,

Jose

 

[Jose]

PS- I'm particularly anoyed when I get a message saying application so
and so can not started because main file can not be found, and then
the next time I boot, it does start automatically, then a few days
latter it no longer does, and finally I need to reinstall the
application.
Can any RAID type fix this for me?

RAID has no way of knowing a file is corrupt, unless the file becomes
corrupt due to failure of the raid or bad sectors on the hard drives,
etc, in which case you might get some sort of error message depending on
your raid / controller setup.

Well, since it stores, parity information, I thought it might/could
use that while reading files to check for their integrity - I know it
would delay the process.

If it would recover, fix, or move the data on bad sectors, that's
something nice, already.

I suppose we're still talking about RAID5 - which is what I originally
asked about - not RAID 1 (or does RAID1 also handle bad sectors
automatically?)

Thanks,

Jose

 

[Rod Speed]

PS- I'm particularly anoyed when I get a message saying application
so and so can not started because main file can not be found, and
then the next time I boot, it does start automatically, then a few days
latter it no longer does, and finally I need to reinstall the application.

You've got some fundamental problem with the hard
drive subsystem, or something very basic like ram etc.

 

[Folkert Rienstra]

Jose wrote in news:[email protected]

Hi All,

With all HDDs working, does RAID5 have any advantage as far as data
integrity is concerned - as when files are being read/written,?
Nope.

Assume, that in 1 hdd, a portion of a file has become corrupted.

Again: hard drives do not corrupt data.

One speaks of corruption when data is returned that doesn't reflect
the original written data. A file can be corrupted if less data is re-
turned than was originally written to it without an error issued. This
won't happen with harddrives as the culprit. It's a system problem.
Files disappearing may be caused by the system not being able to read
directories but fail to tell you so.

While reading that file, will the system parity, or error correction, or
something else, to detected that, and repair the file?

What else did you think redundant in RAID stands for.

 

[Arno Wagner]

On Tue, 26 Feb 2008 19:01:21 +0000, Odie Ferrous

Well, since it stores, parity information, I thought it might/could
use that while reading files to check for their integrity - I know it
would delay the process.

If it would recover, fix, or move the data on bad sectors, that's
something nice, already.

I suppose we're still talking about RAID5 - which is what I originally
asked about - not RAID 1 (or does RAID1 also handle bad sectors
automatically?)

Jose

Jist ot give you an example, here is how it works under Linux:
If a defective sector is found, that one is reconstructed using the
other disks. No other defect detection is done. You can run an offline
integrity check, but it is rather obscure. If enough defects are found
in one disk, then that disk is disabled entirely. If a hot spare
is available, the array is reconstructed using that.

So, yes, if your files are corrucpted because of defective sectors,
then RAID5 will help to some degree. If it is something else, e.g.
defective RAM, RAID5 could not care less.

Arno

 

[Arno Wagner]

PS- I'm particularly anoyed when I get a message saying application so
and so can not started because main file can not be found, and then
the next time I boot, it does start automatically, then a few days
latter it no longer does, and finally I need to reinstall the
application.
Can any RAID type fix this for me?

This sounds like a filesystem issue. RAID5 will likely have no effect
here. But you should do more thorough analysis what the problem
actually is.

Arno

 

[Jose]

Jist ot give you an example, here is how it works under Linux:
If a defective sector is found, that one is reconstructed using the
other disks. No other defect detection is done. You can run an offline
integrity check, but it is rather obscure. If enough defects are found
in one disk, then that disk is disabled entirely. If a hot spare
is available, the array is reconstructed using that.

So, yes, if your files are corrucpted because of defective sectors,
then RAID5 will help to some degree. If it is something else, e.g.
defective RAM, RAID5 could not care less.

Thanks a lot for the clear answer! Hopefuly it works that way in
Windows too ;-)
Naturaly, I wouldn't expect RAID5 to do anything about any potential
memory problem.

Best,
Jose

 

[Jose]

This sounds like a filesystem issue. RAID5 will likely have no effect
here. But you should do more thorough analysis what the problem
actually is.

In other words, please? What do I need to do?

Regards,
Jose

 

[Jose]

What else did you think redundant in RAID stands for.

What just about everybody else has been trying to push into my head:
it's only good one 1 of the hdd stops working, you replace it with a
new one, and the system rebuilds the info on the dead hdd.

Where in the Net can you find a proper explanation of what RAID5 does,
before one of the hdd dies,
*for_people_who_don't_know_the_answer_yet*?

I wouldn't have come asking here if I had been able to find the answer
already written elsewhere...

Regards,
Jose

 

[Folkert Rienstra]

Jose wrote in news:[email protected]

Well, since it stores, parity information, I thought it might/could
use that while reading files to check for their integrity

Gee, there's an idea. Maybe you should patent it. Call it RAID-5.

- I know it would delay the process.

Oh, why's that. (notice the absence of a question mark)

If it would recover, fix,

or move the data on bad sectors,
What.

that's something nice, already.

Already? Just for starters, huh. Any other wishes?

I suppose we're still talking about RAID5 - which is what I originally
asked about - not RAID 1

(or does RAID1 also handle bad sectors automatically?)

It does or doesn't, just as RAID5 does or doesn't, depending
on ones definition of "handle bad sectors automatically".
Whether that includes 'made to disappear' depends on the
features of your particular RAID controller.

 

[Folkert Rienstra]

Jose wrote in news:[email protected]

[On topic info snipped]

Apparently not actually interested.

What just about everybody else has been trying to push into my head:

Uhuh, and who exactly is "everybody else"?

it's only good one 1 of the hdd stops working, you replace it with
a new one, and the system rebuilds the info on the dead hdd.

Nonsense.
When it can do that offline then obviously it can do it online as well,
for a single sector.

Where in the Net can you find a proper explanation of

what RAID5 does, before one of the hdd dies,

The same as after. It works on the sector level.

*for_people_who_don't_know_the_answer_yet*?

Ever heard of FAQ and Google?
Even tried something utterly silly as typing www.raid.com?

 

[Bob Willard]

What just about everybody else has been trying to push into my head:
it's only good one 1 of the hdd stops working, you replace it with a
new one, and the system rebuilds the info on the dead hdd.

Where in the Net can you find a proper explanation of what RAID5 does,
before one of the hdd dies,
*for_people_who_don't_know_the_answer_yet*?

I wouldn't have come asking here if I had been able to find the answer
already written elsewhere...

Regards,
Jose

Google for it. Or go straight to http://en.wikipedia.org/wiki/RAID

If you are looking for early warning of problems with an individual HD
in a RAIDset, you're out of luck: that is beyond the scope of RAID.
Some RAID controllers may keep and report statistics on individual HDs,
but AFAIK there is no standard on how, or even if, they do so.

 

[Jose]

Google for it. Or go straight to http://en.wikipedia.org/wiki/RAID

Been there, done that.

Some RAID controllers may keep and report statistics on individual HDs,
but AFAIK there is no standard on how, or even if, they do so.

I guess IF is the actually the question here, and that's what made me
ask where I thought I might get more/better information than the one I
can find Googling.

Thanks anyway.
Jose