There are many causes of RAID failure. Often a hard drive has failed
and noone notices. By the time another drive in the array fails it's to late and you
no longer have the ability to rebuild the RAID yourself. The term
"redundant" in this case is only accurate when 1 drive has failed. When
more than 1 drive in your array fails it's time for professional help.
At this point, missing one or more of your drives in the RAID you will
only have incomplete/ corrupt data. One of the failed drives must be
rebuilt and the data recovered before the RAID can be completely
We have experience with all types of RAID arrays and can help.
When sending a RAID array in to our lab for data recovery:
The likelihood of a successful recovery increases if we have the actual
computer system and controller card for your RAID. Send us the entire
system if possible.
Number all drives in the array and keep them in the drive bay where
they were when you first noticed the failure. If you lose track of what
drive went where it could complicate the recovery process.
Package the system with several inches of padding around all sides to avoid any further damage in shipping.
for RAID Data Recovery
What is a RAID?
RAID is an acronym for Redundant Array of Independent Disks. A RAID
array is a collection of drives which collectively act as a single storage
system, which can tolerate the failure of a drive without losing data,
and which can operate independently of each other.
Definitions of various RAIDs:
RAID Level 0 is not redundant, hence does not truly fit the "RAID" acronym.
In Level 0, data is split across drives, resulting in higher data throughput.
Since no redundant information is stored, performance is very good,
but the failure of any disk in the array results in all data loss. This
level is commonly referred to as striping.
RAID Level 1 is commonly referred to as mirroring with 2 hard drives.
It provides redundancy by duplicating all data from one drive on another
drive. The performance of a Level 1 array is slightly better than a
single drive, but if either drive fails, no data is lost. This is a
good entry-level redundant system, since only two drives are required.
However, since one drive is used to store a duplicate of the data, the
cost per megabyte is high.
RAID Level 2, which uses Hamming error correction codes, is intended
for use with drives which do not have built-in error detection. All
SCSI drives support built-in error detection, so this level is of little
use when using SCSI drives.
RAID Level 3 stripes data at a byte level across several drives, with
parity stored on one drive. It is otherwise similar to level 4. Byte-level
striping requires hardware support for efficient use.
RAID Level 4 stripes data at a block level across several drives, with
parity stored on one drive. The parity information allows recovery from
the failure of any single drive. The performance of a level 4 array
is very good for reads (the same as level 0). Writes, however, require
that parity data be updated each time. This slows small random writes,
in particular, though large writes or sequential writes are fairly fast.
Because only one drive in the array stores redundant data, the cost
per megabyte of a level 4 array can be fairly low.
This level is commonly referred to as striping with distributed parity.
RAID Level 5 is similar to level 4, but distributes parity among the
drives. No single disk is devoted to parity. This can speed small writes
in multiprocessing systems. Because parity data must be distributed
on each drive during reads, the performance for reads tends to be considerably
lower than a level 4 array. The cost per megabyte is the same as for
Information from Adaptec.com & SUN.com