Re: RAID Class Drives`

[CoolCold <coolthecold@gmail.com>]

On Sun, Apr 18, 2010 at 11:59 PM, Stefan /*St0fF*/ Hübner
<stefan.huebner@stud.tu-ilmenau.de> wrote:
> Hi!
>
> Am 18.04.2010 14:11, schrieb CoolCold:
>> I don't really understand one point - why it failed? Did the
>> controller dropped device because it wasn't responsible or md did
>> this? Rephrasing my question - this is really "tuning" for controller
>> not to drop device and report error or for md?
>
> If a desktop class drive starts its error recovery, it becomes
> unresponsive.  MD thinks this, but it isn't smart.  It tries to rewrite
> the sector while the drive itself is still in error recovery mode and by
> that unresponsive.  The write fails, MD drops the device.
Stop-stop. It is clear that timeouting "read" request in short period
is good idea, but i wanna know about writes
Does write fail because controller returns smth like "media error" or
md has internal operation timeouts?
Even if drive doens't become irresponsible and returns "error on
write" it will be dropped anyway.

So, SCT-ERC setting will prevent drive to be irresponsible for long
time which may be desirable in case of:
a) md doesn't have it's own timeouting mechanism and the whole md
device will be stucked
b) drive ( another partition ) is part of another array/lvm
pv/whatever and that device will be stucked too.


>
>> And if drive has errors anyway, why it shouldn't be dropped, is it for
>> just in case we have read error, we can try to rewrite it from the
>> alive array part? If we have write error, we gonna drop drive from
>> array anyway..
>>
> Because that is the reason hdd manufacturers built in spare sectors and
> internal error recovery procedures.  Think about the write density of
> todays drives, think about the many influences which it must work with.
>  The nearly atomically-sized bits on the platter.
> IT IS NOT POSSIBLE to build a perfect drive on todays specifications.
> That's why this exists in the first place.  And as we can see it is a
> very easy way for hdd manufacturers to make extra money.  Just label
> those drives that also passed the very last quality test (not only the
> other 10 tests before) "superdrive", sell them for nearly double the
> price and give them a firmware, where the advanced features are just
> enabled as default...
>
> /stefan
>
>



-- 
Best regards,
[COOLCOLD-RIPN]
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