Qsan XS5224D User Manual page 131

the throughput of most read and write operations equal to the throughput of one disk
multiplied by the quantity of disk drives. Increased throughput is the big benefit of RAID 0, at
the cost of increased vulnerability of data due to drive failures.
RAID 1 (Mirroring between two disks)
RAID 1 consists of data mirroring, without parity or striping. Data is written identically to two
drives, thereby producing a mirrored set of drives. Thus, any read request can be serviced by
any member drive. Write throughput is always slower because every drive must be updated,
and the slowest drive limits the write performance. The array continues to operate as long
as at least one drive is functioning.
N-way Mirror (Mirroring between N disks)
It's an extension of RAID 1. Data is written identically to N drives, thereby producing an N-
way mirrored set of drives
RAID 3 (Striping, can survive one disk drive fault, with parity on a dedicated disk
drive)
RAID 3 consists of byte-level striping with dedicated parity. All disk spindle rotation is
synchronized and data is striped such that each sequential byte is on a different drive. Parity
is calculated across corresponding bytes and stored on a dedicated parity drive. The data
disperses on a different hard drive, even if you want to read short information, it may need
all the hard drives to work. So this is more suitable for large amounts of read data requests.
RAID 5 (Striping, can survive one disk drive fault, with interspersed parity over the
member disk drives)
RAID 5 consists of block-level striping with distributed parity. It requires at least three disk
drives. Upon failure of a single drive, subsequent reads can be calculated from the
distributed parity such that no data is lost. RAID 5 is seriously affected by the general trends
regarding array rebuild time and the chance of disk drive failure during rebuild. Rebuilding an
array requires reading all data from all disks, opening a chance for a second disk drive
failure and the loss of the entire array.
RAID 6 (Striping, can survive two disk drive faults, with interspersed parity over
the member disk drives)
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Storage Management