Re: Anyone familiar with Apple Xserve RAID

Doug McNaught wrote:

>Kevin Barnard <kbarnard@speedfc.com> writes:
>
>  
>
>>   Actually you are both are right and wrong.  The XRaid uses
>>   FibreChannel to communicate to the host machine(s).  The Raid
>>   controller is a FibreChannel controller.  After that there is a
>>   FibreChannel to UltraATA conversion for each drive, separate ATA bus
>>   for each drive.
>>   What I am curious about is if this setup gets around ATA fsync
>>   problems, where the drive reports the write before it is actually
>>   performed.
>>    
>>
>
>Good point.
>
>(a) The FC<->ATA unit hopefully has a battery-backed cache, which
>    would make the whole thing more robust against power loss.
>(b) Since Apple is the vendor for the drive units, they can buy ATA
>    drives that don't lie about cache flushes.  Whether they do or not
>    is definitely a question.  ;)
>  
>

FYI:    http://developer.apple.com/technotes/tn/pdf/tn1040.pdf   a tech 
note on write cache flushing.

A bit dated now, but perhaps some other tech note from Apple has more 
recent information.

-- Alan