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

Previously Jose <(E-Mail Removed)> wrote:
> 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

Jose wrote:
>
> 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
--
Retrodata
www.retrodata.co.uk
Globally Local Data Recovery Experts

On Tue, 26 Feb 2008 19:01:21 +0000, Odie Ferrous
<(E-Mail Removed)> wrote:

>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

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?


On Tue, 26 Feb 2008 19:01:21 +0000, Odie Ferrous
<(E-Mail Removed)> wrote:

>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 <(E-Mail Removed)> wrote:

> 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.

> Can any RAID type fix this for me?

Nope.


> On Tue, 26 Feb 2008 19:01:21 +0000, Odie Ferrous
> <(E-Mail Removed)> wrote:
>
>> 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 wrote in news:(E-Mail Removed)
> 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.
news:47aa17e7$1$3968$(E-Mail Removed)

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.

>
> Thanks,
> Jose

Previously Jose <(E-Mail Removed)> wrote:
> On Tue, 26 Feb 2008 19:01:21 +0000, Odie Ferrous
> <(E-Mail Removed)> wrote:

>>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


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

Previously Jose <(E-Mail Removed)> wrote:
> 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

On 27 Feb 2008 00:47:54 GMT, Arno Wagner <(E-Mail Removed)> wrote:

>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