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What are the types of RAID ?




Various levels of RAID exist...

RAID0 - Span

Adds the capacity of the disks together to make 1 larger volume.
Minimum 2 disks. e.g. 2*80Gb drives = 160gb volume.
Provides no redundancy - if any disk fails you lose everything.

RAID1 - Mirror

Automatically mirrors the contents of one disk to another identical drive.
Uses 2 disks. e.g. 2*80Gb drives = 80gb volume.
Provides basic redundancy - if a single drive fails it can be removed from eth RAID Array and all the data still exists of the other drive.

RAID5 - Stripe and Checksum

Stripes data across n-1 disks, using the final disk as a checksum drive.
Minimum 3 disks. e.g. 3*80Gb drives = 160gb volume.
Provides standard redundancy, if a single drive fails it can be replaced with no loss of data, as every single disk content can be rebuilt from knowing the contents of the remaining disks.

RAID6 - Stripe and Checksum with HotSpare

Stripes data across n-2 disks, using the one disk as a checksum drive and another as a standby drive.
Minimum 4 disks. e.g. 4*80Gb drives = 160gb volume.
Provides advanced redundancy, if a single drive fails it is automatically rebuilt onto the hotswap spare drive, with no loss of data or downtime, although access times are reduced during the rebuild.

RAID10 (raid1+0) - Span and Mirror

Adds the capacity of half of the disks together to make 1 larger volume. With the added failover of a complete mirror set of those drives.
Minimum 4 disks. e.g. 4*80Gb drives = 160gb volume.
Provides complete redundancy, if any drive fails, the data is simply read from the equivalent drive in the mirror set automatically. No loss of data and no downtime, although access times are not reduced as with RAID6, the failed disk can be replaced and will auto-rebuild.

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