software RAID 1 w/3 Drives

[Dan Lund]

A spare allows the system to hum along at the same data rate without 
living in a constant degraded state.  The idea is to keep it "business 
as usual" even with a disk failure... where if you lose a disk in a 
spare-less raid1 setup, there's a degraded performance because it's 
doing things behind the scenes to keep things in check so when the raid 
array has a disk added it can replicate back to it properly.

If you buy the disks in the same batch, you run the risk of them dying 
at the same time, also... so that's another thought when doing raid.

Shawn Badger wrote:
> That is why it is nice to have the mirror and the data replicated to 
> another disk. But what are the chances of loosing 3 disk on the same 
> system within such a short time frame that you would not be able to 
> replace a single disk that failed? The only time I have ever heard of 
> loosing more than one disk in a day has been due to some type of power 
> surge that usually fried the server has well.
>
> On 7/24/07, *Dan Lund* <situationalawareness at gmail.com 
> <mailto:situationalawareness at gmail.com>> wrote:
>
>     It's only a waste until you lose disks.....
>     Then you thank your lucky stars you have it.
>
>     Shawn Badger wrote:
>     > So you are saying that the data is replicated 3 times to each drive.
>     > Drives are cheap, but that seems to be a waste to me.
>     >
>     > Just my 2 cents thought.
>     >
>     > On 7/23/07, * JT Moree* <moreejt at pcxperience.com
>     <mailto:moreejt at pcxperience.com>
>     > <mailto:moreejt at pcxperience.com
>     <mailto:moreejt at pcxperience.com>>> wrote:
>     >
>     >     -----BEGIN PGP SIGNED MESSAGE-----
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>     >
>     >     Shawn Badger wrote:
>     >     > The 3 drives as a Raid is probably set up to have on as a hot
>     >     spare. A
>     >     > four drive Raid 1 is not really a Raid 1 it is either a
>     Raid 01
>     >     or more
>     >     > likely a Raid 10. In a Raid 01 you stripe a pair of drives
>     and then
>     >     > mirror the striped drives. The more common configuration
>     is to
>     >     create
>     >     > two mirror sets and then stripe them. This gives you fault
>     >     tolerance
>     >     > with high though put.
>     >
>     >     No,  It's four mirrored drives.  if the boot drive
>     fails.  The other
>     >     drives have lilo in the mbr so they will boot from the
>     mirrored boot
>     >     partition--the same on every drive.
>     >
>     >     - --
>     >     JT Morée
>     >     PC Xperience, Inc.
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