Tag raid 10 for speed

The incredibly odd winter weather in our area continued last night.  Winter in Florida usually means high temperatures in the 70’s, blue skies, and long, long stretches of no precipitation whatsoever.  This morning we woke up to SEVERE standing water on our property, possibly more than we saw at any point during the summer rainy season.  I woke up several times during the night from the sound of hard rain but it still did not prepare me for the very wet landscape pictured above.  Winter is not supposed to be about sloshing through ankle high water.  The chickens will get to work on their swimming skills today.

Yesterday I got a couple automated messages on my home phone supposedly from the IRS, stating they were filing a lawsuit against me.  A quick Google search revealed this has been an ongoing scam for quite awhile and can be safely ignored.  It seems unreal to me that the perpetrators of this scam are able to do so for months on end without any repercussions.  Sadly there are surely some people that have fallen for this scheme, after all the words “lawsuit” and “IRS” make for a potent combination.

I am in the process of building a new application server for the office.  It is going to be the first time I will be implementing a RAID 10 configuration for the hard drive array.  One of the most vulnerable parts of a computer is the hard drive which consists of platters spinning as fast as 15k rpm’s 24 hours a day.  In order to provide protection from hard drive failure, servers normally have multiple hard drives that use RAID (redundant array of inexpensive disks).  There are different type of RAID that are identified by number.

RAID 5 is what I have used for most of my IT career.  In this configuration you need a minimum of 3 hard drives.  RAID 5 allows you to lose any one of the drives to failure and not lose your data.  If a drive goes bad you can remove it, slap in a new drive and not lose a beat.

With RAID 5 there are some drawbacks. The parity bit stripe that has to be written across all disks inflicts a performance penalty.  Also when a new drive is inserted to replace a dead one, the rebuild process is very resource intensive, causing server performance to drag.  The rebuild also hammers the good disks, in some rare situations the rebuild process is intense enough that it will cause a SECOND drive to fail in the middle of it.  (this has happened to me)  If you lose a second drive it is game over.

There is RAID 6 which uses a similar method that requires a minimum of 4 drives but will allow you to lose up to two drives and still have your data intact.  The con of this is even more of a write/read and rebuild penalty than RAID 5 has.

The server I am working on will have a total of 12 hard drives, 10 of which will be used for a RAID 10 array.  The remaining 2 drives will be “hot spares”, meaning if a drive goes bad one of the spares will be fired up and used in the array automatically.  RAID 10 uses a combination of data striping and mirroring which gives you MUCH better performance than RAID 5 or 6.  In my situation with 10 drives I have 5 mirrored drive sets in the array.

The con to RAID 10 is you lose HALF of your drive capacity to redundancy.  In my situation my 40 terabytes of drives will only deliver 20 terabytes of usable space.  RAID 10 can only be guaranteed to be able to lose 1 drive without data loss but potentially could lose more drives and still function depending on your luck.  Since the drives are in mirrored pairs, as long as you don’t lose both drives in a mirror you are still ok.  So in my situation, in theory, I could lose as many as 5 drives and still have my data intact.  Of course that would require incredibly good luck.

Now I assume the vast majority of the blog audience won’t really be interested in server RAID discussion but it just happened to be the thing on the top of my thought barrel today so that is what comes out.