RAID Recovery Information:
We specialize in Raid Data
Recovery service.
We have 95%
success rate in the Recover Industry.
RAID systems may be
fault-tolerant, but they are not fault proof. While most commercial RAID
implementations can tolerate the loss of a single hard drive,
if multiple hard drives fail, or other serious
problems occur, RAID data recovery may be necessary.
With their built-in
redundancy, RAID systems are able to continue functioning even if a hard
drive fails. When this happens however, performance is negatively affected,
and the RAID is said to be operating in a degraded, or critical state.
This occurs because the lost information must be regenerated "on the fly"
from the parity data.
When a failed drive is
replaced, the data that was removed from the array with its departure must
be regenerated on the new disk by the RAID controller, a process called
rebuilding. An array is vulnerable while it is running in a degraded state.
Until the failed drive is replaced and its data rebuilt, the array
provides no redundancy.
RAID systems are susceptible
to the same ailments that plague single hard drives, such as viruses,
logical problems, human error, and physical damage. Moreover, due to their
complexity, they may suffer from additional points of failure, such as lost
server registry configurations, accidental RAID drive reconfigurations, RAID
controller failures and multiple drive failures.
If multiple drives fail,
or other serious problems occur in a RAID, your data may be compromised.
Under such circumstances, if
you fail to make a proper backup, you may have to call US. We have high
success rates when it comes to RAID data recovery. Using specialized
facilities, equipment, and software, we can even recover data from a
moribund hard drive.
You have come to the
right place. Our success rate is typically above 95% and our charges are
very reasonable for the effort involved. We are able to recover data from
drives where a head crash has physically damaged part of the platter. Our
clean room environment allows us to access the sealed portions of hard
drives and correct failed internal components. In most cases, the recovery
process involves restructuring of the data using highly sophisticated
techniques and proprietary equipment and software our engineers have
developed. Our special RAID recovery tools reconstruct the data when
standard RAID rebuild processes fail. We can recover data from both hardware
and software RAIDs.
We follow a standard set of
RAID data recovery procedures. This usually includes an initial evaluation,
where technicians carefully examine the array to diagnosis the exact nature
of the problem. During this time, they'll also attempt to make an image of
the failed hard drives. The RAID data recovery specialists will then extract
the data from the image, and work to piece it together. If successful, they
will restore your data onto the media of your choice.
Striping is a technique which offers the best performance of any RAID
configuration. In a striped array, data is interleaved across all the
drives in the array.
An analogy may be helpful in understanding how striping works.
Imagine you asked a friend to write down all the numbers between 0 and
100. It would probably take him a few minutes to jot them all down. Now
imagine that instead of asking just one friend to write down the numbers,
you asked ten friends to divide the numbers up equally amongst themselves so
that one writes down 0 to 9, another 10 to 19, and so on and so forth until
all were assigned a task. It would take a fraction of the time. This is how
striping works. By splitting up the data and distributing it across multiple
drives, you increase performance.
Performance in a striped array is dependant on the stripe
width (the number of drives in the array) and the stripe size (the size
of the chunks of data being written across the array). Striping can occur
at two different levels: byte level and block level. Byte
level striping involves breaking up the data into bytes and storing them
sequentially across the hard drives. Block level
striping involves breaking up the data into a given block size. These blocks
are then distributed in the same way across the array as in byte level
striping.
So, what stripe size should you use to wring the most performance out of
your RAID? Well, that depends on what type of application you're using it
for.
Larger stripes mean fewer accesses to the disk. For this reason, larger
stripes are useful for I/O-intensive (Input/Output) applications such as
database servers. Smaller stripes on the other hand, mean that data can be
accessed more quickly because data chunks are smaller. Consequently, smaller
stripes are better suited for throughput-intensive applications such as
video production and editing.
Although a striped array may offer the best performance of any RAID
configuration, it provides no redundancy. If one drive in the array fails,
all of your data will be lost and you may need to consider RAID data
recovery options.
That's where mirroring comes in. With mirroring, whatever you write to
one drive, gets written simultaneously to another. Thus, you always have an
exact duplicate of your data on the second drive. This is one of the two
data redundancy techniques used in RAID to protect you from data loss. The
advantage of this technique is that when one hard drive in the array fails,
the system can still continue to operate since there are two copies of the
data. Downtime is minimal and rebuilding the data from the good copy is
relatively easy.
Mirroring also provides a small performance boost over a single
non-arrayed drive. Since the mirrored pairs contain the same data, the RAID
controller can read data from one drive while simultaneously requesting data
from the other. Of course, write speeds will be slower than with other
techniques because data must be written twice, once on each drive.
Parity is an error correction technique commonly used in certain RAID
levels. It is used to reconstruct data on a drive that has failed in an
array.
Here's how it works: your RAID controller adds a parity byte to all
binary information being written to the array. Basically, this is just an
extra byte of data tacked onto the actual data. These parity bytes are
added up by the controller to equal either an even or an odd number. By
analyzing this value, the controller can determine whether the information
has been compromised in any way. If it has, it can replace the data
automatically with data from the other drive.
You may be wondering how the parity data is created in the first place.
Well, typically it's done using a logical operation called
eXclusive OR (XOR). Basically, the controller analyzes the series of 0's
and 1's which make up the data, and returns either a TRUE (for even numbers)
or FALSE (for odd ones). By using this data, it can "fill in the blanks".
It's like being back in your high school algebra class. You know that 3 + 6
= 9. If you see the equation 3 + _ = 9, you know the blank is supposed to be
a 6. The XOR logic is used in this way to rebuild corrupted data on the
array, thus maintaining integrity.
RAID 0
RAID 0 is considered by many purists not to be a true RAID level because
it lacks the all important "R." RAID 0 provides no redundancy, and as
such, should never be used for applications where data is critical. If a
single hard drive fails in this configuration, RAID recovery may be
necessary, because the loss of even one drive will result in all data in the
array being lost.
Because it only involves striping, RAID 0 is one of the simplest levels
of RAID to implement. It requires at least 2 hard drives, but as long as
both drives are identical, no storage space is wasted. RAID 0 delivers the
best performance and data storage efficiency of any RAID level.
Figure 0. In RAID 0, data is is broken down into stripes which are
written across all the drives in the array.
RAID 1
RAID 1 employs the mirroring technique. As a result, it uses storage
space very inefficiently. Fifty percent of your disk space will always be
wasted in a RAID 1 configuration. However, it does offer the advantage of
100% redundancy. If one disk fails, there's no need to call a RAID recovery
company to recover your data, simply rebuild your lost data from the mirror.
RAID 1 requires at least 2 hard drives, and additional hard drives must
always be added in pairs. It is ideal for applications where data is
critical.
Figure 1. In RAID 1, data from one hard drive is mirrored onto a
second hard drive, so that there are two identical copies of the data.
RAID 2
RAID 2 is the black sheep of the RAID family in that it doesn't use one
or more of the standard striping, mirroring, or parity techniques. It does
however, use something similar to striping with parity, which we'll read
when we cover RAID Level 3.
Because of its high cost and complexity, RAID 2 never really caught on.
In fact, it isn't even used commercially today. RAID 2 uses byte level
striping with a form of error correcting code (ECC) known as Hamming code.
The number of hard drives required for a RAID 2 configuration may vary, but
a typical setup may use as many as 14 disk drives: 10 data disks and 4 ECC
disks.
Figure 2. In RAID 2, data is split at the bit level over a number of
data and ECC disks. Every time data is written to the array, the Hamming
codes are calculated and written to the ECC disks. When the data is read
from the array, these ECC codes are read as well to confirm that no errors
have occurred since the data was written. If a single-bit error occurs, it
can be corrected immediately.
RAID 3
RAID 3 has a lot in common with its younger brother RAID 2 in that it
also uses byte level striping and a dedicated parity disk. Where the
siblings part company however, is in their error correcting methods. While
RAID 2 uses Hamming code ECC, RAID 3 uses the more effective XOR algorithm
to generate parity.
Unlike the previous levels we've seen, RAID 3 is a practical solution
that delivers good performance and fault tolerance. The dedicated parity
disk does slow down write speeds though, because the parity information has
to be written to the parity drive whenever a write occurs. RAID data
recovery however, is not as big an issue with this implementation.
RAID 3 requires at least 3 hard drives.
Figure 3. Under RAID 3, data is striped at the byte level, across
multiple disks. The parity information is sent to a dedicated parity disk,
but the failure of any disk in the array can be tolerated.
RAID 4
RAID 4 is very similar to RAID 3. In fact, it's so similar that people
often confuse the two. There is one major difference between them however:
RAID 4 uses block level striping. The advantage of block level striping is
that you can change the stripe size to suit your application needs.
RAID 4 requires at least three hard drives. Like RAID 3, it offers good
performance and fault tolerance, and RAID data recovery isn't as much of a
concern. The dedicated parity disk however, remains the bottleneck.
Diagram 4. RAID 4 improves performance by striping data across many
disks in blocks. It provides fault tolerance through a dedicated parity
disk.
RAID 5
The most popular member of the RAID family, RAID 5 combines block level
striping with distributed parity for good performance, fault tolerance and
storage efficiency. This level minimizes the write bottlenecks of RAID
levels 3 and 4, by distributing parity stripes over a series of hard drives.
In doing so, it provides relief to the concentration of write activity on a
single drive, which in turn enhances overall system performance.
RAID 5 is often used as an all-purpose RAID solution, but it is also used
for database and file server applications.
RAID 5 requires a minimum of three hard drives, but often costs less to
implement than RAID 3 or 4. RAID recovery may be necessary if more than one
disk fails.
Diagram 5. In RAID 5, data and parity information are striped in
blocks across all the drives in the array. Fault tolerance is maintained by
ensuring that the parity information for any given block of data is placed
on a separate drive from those used to store the data itself.
Below is a summary of some of the features of the RAID levels we've
discussed. There are of course, many more RAID levels that exist, which
aren't listed.
Table 1. RAID Level Summary
|
Level |
Techniques |
Description |
Min.
Drives |
Failure
Conditions |
Pros/Cons |
Uses |
|
RAID O |
Disk
striping (no fault tolerance) |
Data is
broken into stripes which
are sent to each disk in the array. |
2 |
When one
drive fails, the entire array is compromised. |
Offers Best
performance
No fault tolerance. |
Video editing
and production |
|
RAID 1 |
Disk
mirroring |
Data on one
drive is mirrored on another. |
2 |
If one drive
fails, data is not lost. If both drives fail, the data is lost. |
100%
redundancy of data/Slower performance and 50% loss of storage space. |
Accounting,
payroll, financial |
|
RAID 2 |
Byte level
striping with Hamming code ECC |
Data is split
at the bit level over a number of data and ECC disks. |
Up to 14+ |
Only one
drive may fail and still be recoverable "on the fly". |
On the fly
data error correction/Extremely high cost. |
No commercial
uses |
|
RAID 3 |
Byte level
striping with dedicated parity |
Data is
striped at the byte-level, across multiple disks. |
3 |
When more
then one drive fails, the array is compromised. |
High
read/write data transfer rates/Complex controller design |
Image and
video editing |
|
RAID 4 |
Block level
striping with dedicated parity |
Data is
striped in blocks across data disk, with parity store on a separate
disk. |
3 |
When more
then one drive fails, the array is compromised. |
High
Read/Low Write data transaction rates. |
General
purpose |
|
RAID 5 |
Block level
striping with distributed parity |
Data and
parity are striped in blocks across all disks. |
3 |
When more
then one drive fails, the array is compromised. |
High Read
data transaction rates/ Complex controller design |
Web, database
or file servers |
|
HARD DRIVE CRASH
