RE: Quick Survey

Joe,

Just a quick point...

But when dealing with RAID5, if you have 8 drives, you have a choice of 1x8 
array or 2x4 array.  Statistically speaking, if a 1x8 array and two failed 
drives you have a 100% chance of data loss.  But with 2x4, you have only a 43% 
chance of data loss.

Thought you might find it interesting/helpful.

Charles Wilt
--
iSeries Systems Administrator / Developer
Mitsubishi Electric Automotive America
ph: 513-573-4343
fax: 513-398-1121
 

> -----Original Message-----
> From: midrange-l-bounces@xxxxxxxxxxxx
> [mailto:midrange-l-bounces@xxxxxxxxxxxx]On Behalf Of Joe Pluta
> Sent: Friday, September 02, 2005 3:29 PM
> To: 'Midrange Systems Technical Discussion'
> Subject: RE: Quick Survey
> 
> 
> 
> Seems to me the exposure on these are very close to equal.  
> The chances
> of losing two drives is miniscule, and there's just about as 
> much chance
> of losing two in the same RAID1 set as losing two anywhere in a RAID5
> set (I know it's not mathematically the same, but from an order of
> magnitude position, you can kill a RAID1 set almost as easily 
> as a RAID5
> set).
> 
> 
> 
> This is probably a reasonable option for mission critical H/A systems.
> RAID50 is the fastest and most redundant system.  However, it requires
> quite a bit of extra disk; as much as 200% overhead worst case.
> 
> 
> 
> And redundant Internet connections and everything else.  Different
> league.  Again, that's why I was specifically talking about RAID1 vs.
> RAID5.  These seem to be the reasonable choices for anything 
> short of a
> realtime mission critical system.
> 
> Of course, the next discussion is hot-swap vs. non-hot-swap 
> <g>.  Again,
> for a non-mission-critical system where loss of work is more important
> than interrupted service, it seems that hot-swap is an unnecessary
> expense.  On the other hand, the ability to quickly replace a failing
> drive before a second one goes casters up is probably a good reason to
> have hot-swap bays in HA environments.
> 
> Joe
>