RAID levels


A

ade

Hi - quick question, have these standards been changed lately?

I always was taught, and read, that raid 0 was disk striping acroos multiple
disks of the same size, but you had no fault tolerance and you only 'saw'
one disks capacity. Not a volume set, where all the disks capacity are
added together to form a large volume.

Raid 1 - disk mirroring

Would that mean that raid 1/0 was a stripped set that is mirroed for some
fault tolerance, or something else.

Can someone please confirm this for me?
TIA
 
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R

Rob Stow

ade said:
Hi - quick question, have these standards been changed lately?

I always was taught, and read, that raid 0 was disk striping acroos multiple
disks of the same size, but you had no fault tolerance and you only 'saw'
one disks capacity. Not a volume set, where all the disks capacity are
added together to form a large volume.

Raid 1 - disk mirroring

Would that mean that raid 1/0 was a stripped set that is mirroed for some
fault tolerance, or something else.

0+1 is a striped set that is mirrored.
1+0 is a mirrored set that is striped.

If all drives are on the same controller, it doesn't much matter
which is used. However, if two controllers are available then
normally one stripe set is on each controller - and if there are
more than 2 drives in each stripe set it gets a little messy to
do it any other way.
 
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C

Colon Terminus

You were taught and read wrong.

RAID 0 is indeed disk striping where data is spread across multiple drives
and there is no fault tolerance. You will see the stripe set capacity as
double the smallest disk capacity in the set. In other words two disks, one
with a capacity of 80GB and one with a capacity of 120GB, when striped will
yield an apparent capacity of 160GB (twice the capacity of the smallest disk
in the array). The remaining 40GB will be forever lost and unusable.

RAID 1 is a mirror set. The capacity of the mirror is the capacity of the
smallest disk in the array.

RAID 0/1 or 1/0 is a mirrored stripe. This consists of two RAID 0 stripe
sets that, following the above rules, are hardware mirrored.

RAID 0 offers almost double or beter read/write speed.
RAID 0 requires at least two similar disks.
RAID 1 offers somewhat increased read speed with write speed limited to the
slowest disk in the array.
RAID 1 requires two similar disks.
RAID 0/1 or 1/0 offers both increased read speed and increased write speed.
RAID 0/1 or 1/0 requires at least four similar disks.
 

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