Re: Hilfe: bei linux software raid5 2!! Platten rausgeflogen

Mario 'BitKoenig' Holbe schrieb:

> Sie lebt nicht damit, sie gibt einen Lese-Fehler zurueck und wird
> daraufhin aus dem RAID-Verbund geschmissen.

Belügt uns also WDC?

"The Problem

ATA drives being 'dropped' from a RAID volume was a commonly heard
complaint regardless of manufacturer of the hard drive (that is, until
WD delivered TLER).

....

A drive under a continuous I/O load and performing its own error
recovery can easily exceed 8 seconds of timeout, during which the
normal desktop hard drive does not respond. Although there is no
industry standard, RAID cards will typically wait 8 seconds for a drive
to respond, and if the drive does not respond, RAID cards are
programmed to take action. The 'mis-coordination' of error handling
occurs when desktop drives are programmed to take responsibility for
all error recovery; while RAID cards are /also/ programmed to take
responsibility for error recovery.

The consequence of this mis-coordinated error handling are significant.
After the drive has been dropped from the RAID volume, the RAID volume
runs in degraded mode until a replacement drive is supplied. After a
replacement drive is supplied, assuming it is configured as a RAID 5
volume, the RAID volume must be rebuilt from parity data.

....

The solution

....

TLER-capable hard drives will perform the normal error recovery, and
after 7 seconds, issue an error message to the RAID controller and
defer the error recovery task until a later time.

With coordinated error handling, the hard drive IS NOT DROPPED FROM THE
RAID ARRAY, THEREBY AVOIDING THE ENTIRE RAID RECOVERY, REPLACEMENT,
REBUILD AND RETURN EXPERIENCE.

The error handling is further coordinated between the TLER-capable hard
drive and the RAID card. The TLER-capable hard drive will respond
without waiting on the error to be resolved. RAID CARDS ARE VERY
CAPABLE OF HANDLING THIS WITH A COMBINATION OF PARITY PROTECTION AND
JOURNALING. THE RAID CARD FLAGS THE ERROR IN THE ERROR LOG AND PROCEEDS
TO DELIVER DATA USING PARITY PROTECTION UNTIL THE DRIVE RETRIES ITS OWN
ERROR RECOVERY AND CORRECTS THE ERROR. This is quite similar to error
management proven in SCSI-RAID for many years. It is important to
realize TLER-capable hard drives should not be used in non-RAID
environments."

(Hervorhebungen von mir.)
Quelle: http://www.wdc.com/en/library/sata/2579-001098.pdf

> > Und genau damit kann der user auch besser leben, denn ein defekter
> > Sektor, um den sich dann die Plattenelektronik kümmern kann ist besser
>
> Sie kuemmert sich eben genau nicht darum, sondern gibt schneller auf.

Um nicht aus dem RAID-Verbund geworfen zu werden, und ihre
Korrekturversuche später fortsetzen zu können. So jedenfalls die von
mir oben zitierte Auskunft von WDC. Labern die also Müll? Warum
sollten die Platten bei der Fehlerkorrektur "schlampen", nur um
letztendlich doch aus dem RAID-Verbund geschmissen zu werden? Fieser
Marketing-Trick von WDC?

.

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