Comments on: What are the different RAID levels for Linux / UNIX and Windows Server?

By: Keld Simonsen

Keld Simonsen — Thu, 18 Dec 2008 13:24:37 +0000

There is a wiki for Linux Raid at http://linux-raid.osdl.org – it describes a RAID10 level which is quite like what you describe here as RAID10 or more correctly as RAID1+0, but it is not nested and in some common uses it is double as fast as RAID1+0.

By: BenG

BenG — Thu, 06 Nov 2008 17:30:42 +0000

What about RAID 5+0 and a hot spare?

By: TomasM

TomasM — Wed, 22 Oct 2008 15:55:51 +0000

It looks that with increasing HDD capacities RAID 5 will be not able to provide data safety…

Very good article: Why RAID 5 stops working in 2009 at blogs.zdnet.com/storage/?p=162&tag=nl.e539

“With a 7 drive RAID 5 disk failure, you’ll have 6 remaining 2 TB drives. As the RAID controller is busily reading through those 6 disks to reconstruct the data from the failed drive, it is almost certain it will see an URE.

So the read fails. And when that happens, you are one unhappy camper. The message “we can’t read this RAID volume” travels up the chain of command until an error message is presented on the screen. 12 TB of your carefully protected – you thought! – data is gone. Oh, you didn’t back it up to tape? Bummer!

So now what?
The obvious answer, and the one that storage marketers have begun trumpeting, is RAID 6, which protects your data against 2 failures. Which is all well and good, until you consider this: as drives increase in size, any drive failure will always be accompanied by a read error. So RAID 6 will give you no more protection than RAID 5 does now, but you’ll pay more anyway for extra disk capacity and slower write performance.”

By: vivek

vivek — Wed, 22 Oct 2008 11:23:42 +0000

Overand,

The faq has been updated. Thanks for your post.

By: Overand

Overand — Wed, 22 Oct 2008 06:11:52 +0000

I beg to differ – RAID 5 is not used for database servers- there is a significant “write penalty” for small writes – the entire stripe across all of the drives in the array must be written to. There is even a group called “BAARF” – Battle Against Any Raid Five – – that is basically a bunch of database admins who are horrified at the usage of raid 5 in inappropriate situations.

Database *backups* – sure. But not live databases.