Western Digital WD ShareSpace User Manual page 142

RAID (Redundant Array of Independent Drives) refers to an array of multiple
independent hard drives that provide high performance and reliability. RAID function
depends on the number of drives present and the RAID level selected.
The WD ShareSpace supports the following RAID levels:
• RAID 0 (Striped) — provides data striping (spreading out blocks of each file
across multiple hard drives) but no redundancy. This improves performance but
does not deliver fault tolerance. If one drive fails then all data in the array is lost.
• RAID 1 (Mirrored) — provides disk mirroring. Mirroring creates an exact copy
(or mirror) of a set of data on two drives, which increases reliability compared to a
single drive. If either drive fails, the other continues to function as a single drive
until the failed drive is replaced.
• Two Mirror — Two Mirror mode is available when four drives are installed in the
WD ShareSpace. In this mode, two independent RAID 1 volumes are created.
• Span (Spanned) — combines drives into a linear fashion to create one large
logical volume. Unlike RAID 0, which "stripes" all data bitwise to all drives, the
volume is linear across both drives. A spanned drive is literally like a single bigger
drive, in that files written to the volume earlier go to the "beginning" of the volume,
on the first physical drive. As the volume fills, files written later are written toward
the "end" of the volume, on the second drive. Like RAID 0, no data redundancy is
provided. If one of the drives fails, all data is lost.
• RAID 5 — requires a minimum of 3 drives to implement. Similar to RAID 0 but
adds fault tolerance by including parity information with the data. Parity is
generated on Writes, recorded in a distributed location, and checked on Read. In
this mode, failure of a single drive does not cause loss of data.
• RAID 10 — requires a minimum of four drives to implement. Provides data
striping on top of disk mirroring.
NETWORK STORAGE MANAGER: ADVANCED MODE - 137
WD SHARESPACE
USER MANUAL