36.4GB drive formats out to 32.8GB? what am I missing please grep sectors /var/run/dmesg.boot

D. Goss lists at dylangoss.com
Tue Jun 14 17:51:06 GMT 2005

On Jun 14, 2005, at 8:48 AM, Wojciech Puchar wrote:

> think twice before making RAID-5 array. are you sure small writes  
> will not be too common?

No, you are on to something - I will be making small writes / parity  
calculations.  This is going to be a web server but it is for clients  
and they do have sites running with SQL backends and not just static  
HTML content.

> i think buying 4 80GB FAST IDE/SATA drives and arranging it as  
> RAID-10 will give you 160GB of FAST and protected storage.  
> performance gain using mirror+strip will likely offset this of  
> using faster 15k rpm drives.
> and it will be for sure cheaper. you may put 6 drives (RAID-10) and  
> even larger drives and still have cheaper alternative and even  
> faster. and MUCH more space.

Sure, it will be cheaper.  For me it's too late, I've purchased the 4  
x SCSI 15k drives I need for this project.  I have bought mostly  
unopened, in-box but secondhand IBM drives/sleds.  They are still  
expensive but certainly not the (what I consider) insane prices for  
the same drives IBM direct.  I'm paying around 1/3 of "list".

I'm curious as to if you're right, I'll certainly have something to  
run some benchmarks on soon.  Keep in mind this is all running though  
hardware raid (IBM ServeRAID 6i).  Somehow I feel that 15k SCSI on  
U320 being processed as RAID-5 with this card will be better than you  
state.  You're right, it will have cost more than IDE but I wanted to  
give this approach a try.

Worst thing is that I can fall back to SCSI 1+0 as you suggest at the  
cost of one drive's space.  My guess is that while the drives are  
clean I will play with both structures for the RAID and compare some  
benchmarks to give me an idea of what kind of hit the parity is  
costing me.

Thanks for you comments.


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