Re: Spares and partitioning huge disks

On Saturday 08 January 2005 19:55, you wrote:

My warning about user error was not targeted at you!  :)
Sorry if it seemed so.

:-)

And the order does not matter!

Hm... yes you're right. But adding the disk is more prudent (or is it?)

Grr. Now you've got ME thinking !  ;-)

Normally, the minute a drive fails, it gets kicked and the spare would kick in 
and md syncs this spare.  We now have a non-degraded array again.
If I then fail the spare first, the array goes into degraded mode. Whereas if 
I hotadd the disk, it becomes a spare. Presumably if I now fail the original 
spare, the real disk will get synced again, to get the same setup as before.
But yes, you're right; during this step it is degraded again. Oh well...

It would be cool if the rebuild to the repaired disk could be done before
the spare was failed or removed.  Then the array would not be degraded at
all.

Yes, but this would be impossible to do, since md cannot anticipate _which_ 
disk you're going to fail before it happens. ;)

If I ever re-build my system, or build a new system, I hope to use RAID6.

I tried this in last fall, but it didn't work out then. See the list archives.

The Seagate test is on-line.  Before I started using the Seagate tool, I
used dd.

I'm not as cautious as you are. I just pray the hot spare does what its 
supposed to do.

My disks claim to be able to re-locate bad blocks on read error.  But I am
not sure if this is correctable errors or not.  If not correctable errors
are re-located, what data does the drive return?  Since I don't know, I
don't use this option.  I did use this option for awhile, but after
re-reading about it, I got concerned and turned it off.

Afaik, if a drive senses it gets more 'difficult' than usual to read a sector, 
it will automatically copy it to a spare sector and reassign it. However, I 
doubt the OS gets any wiser this happens, so neither would md.
In which cases the error gets noticed by md I don't precisely know, but I 
reckon that may well be when the error is uncorrectible.
Not _undetectable_, to quote from another thread... 8-)  

This is from the readme file:
Automatic Read Reallocation Enable (ARRE)
        -Marreon/off  enable/disable ARRE bit
           On, drive automatically relocates bad blocks detected
           during read operations.  Off, drive creates Check condition
           status with sense key of Medium Error if bad blocks are
           detected during read operations.

Hm. I would definitely ENable that option.  But what do I know.

It also depends I guess on how fatal reading bad data undetected is for you. 
For me, if one of my mpegs or mp3s develops a bad sector I can probably live 
with that. :-)

Maarten