Re: "raid" versions of hard drives for software raid?

[Roger Heflin <rogerheflin@gmail.com>]

Dan Christensen wrote:
> Dan Christensen <jdc@uwo.ca> writes:
> 
>>> Dan Christensen wrote:
>>>> I'm looking at either the Western Digital 500G RE2 drives or the cheaper
>>>> 500G SE16 drives.  I have read that for use with a hardware raid card,
>>>> the RE2 drives are more appropriate, and I'm wondering if the same is
>>>> true for software raid.
>> The difference that is most commonly described, and that I should have
>> highlighted, is TLER: Time-Limited Error Recovery.  Apparently, the SE16
>> drives can take a long time to recover from an error (up to two minutes,
>> I believe), and hardware raid controllers can kick the drives out of the
>> array when it would instead be better for the drive to return a
>> read/write error and let the raid controller deal with it.
>>
>> My question is really whether this logic applies to linux software raid.
> 
> One more reference:
> 
>   http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery
> 
> It certainly sounds to me like TLER is also appropriate for software
> raid, so I'm going to go ahead and get the RE2 drives.
> 
> Dan

If you were trying to salvage as much data as possible off of a drive TLER would 
also be nice, since it would lower the time to get a bad sector error.

I don't really understand how much use it is to try that many times, the drive 
should be able to try 1x per rev, so at 7200, 120 times per second, I would 
wonder how many times that they get a good read after having failed the first 
120 times, much less after the first 7 seconds (960 failures) of trying, or even 
longer periods without TLER.

In fact I would think for a RAID drive one would want even lower than 7 seconds.

                                 Roger