Raid Recovery and Data Recovery Intro

No system is entirely fail-safe. In fact, as communication technology gets better, it becomes even more important that stored data is as safe as possible using raid, raid recovery, data recovery and data recovery raid is important.

Sometimes, accessing information; both input and output can be a problem, so data recovery is a must for systems.

The Benefits Of Raid Recovery In Data Storage

RAID (redundant array of independent disks) recovery is a way of ensuring that data performance is improved.

RAID recovery is a virtual data storage technology that uses multiple disk drives to ensure optimal data performance.

In disk drives, data is distributed in several ways to utilize techniques of stripping, parity or mirroring.

In disk mirroring, logical disk volumes are replicated onto separate physical hard disks to make sure that data is continuously available.

The mirrored volume completely represents the separate volume and is also completely logical. Mirroring is used in RAID 1.

In data stripping, data is sequential data are segmented logically. This is done so that consecutive segments are stored on different storage devices.

The data segments are spread across multiple physical storage devices, and these devices can be accessed concurrently.

Parity is a technique used in storage to make sure that fault tolerance is provided in data storage.

If any of the drives fails, the missing blocks will be recalculated. It is utilized in checksum and stripping methods.

In RAID the data is distributed in several ways across drives. These ways are called RAID levels.

In RAID recovery, the different data distribution layout or schemes are named as RAID followed by a number.

Every level has a different reliability, performance, capability, and availability. The higher the RAID recovery level, the better the protection against unrecoverable read errors, and against total failure of physical drives.

Data Recovery Raid

Most of the RAID levels make use of parity to provide fault tolerance in data storage. This is done effectively using parity method.

RAID recovery can also be used on solid state drives (SSD), even if the system is not all SSD based. The SSD can be mirrored using a mechanical drive. The different RAID recovery levels are the 0, 1, 2, 3, 4, and 5.

RAID 0 recovery

In the level 0 recovery, the data blocks are stripped between two disks. The blocks are typically 64kB (128 sectors). The first disk (disk 0) will contain sectors 1 through 127.

The second disk (disk 1) will contain sectors 128 through 255. This whole sequence will be alternated throughout the virtual disk.

In this recovery case, an offset is the common complication. Having some sectors before the first striped block gives rise to an offset.

To fix this, search for where the sector number is on the partition table, then clone the disk to another file starting with this sector.

Next, find the stripe size. Make sure you get the stripe size correctly. In most cases, the stripe size is the same as the size of the card used.

After finding the stripe size, you will need to find the break point. To identify a stripe break point, identify a sector, divide the sector by the stripe size.

If the result has decimal points, take just the whole number part. Neglect the figures after the decimal point. Next, multiply this result by your stripe size. The result may be the stripe break point.

In some cases, though, the stripe break point is not that easy to locate, you may have to go through the sectors to be able to locate a break point.

It will be necessary to attentively train your eyes to identify inconsistencies in data as you scroll through the sectors.

If the data is too inconsistent, you may have to go through several areas or portions of the disk to identify the correct stripe break point.

Once the break point is discovered, the process of de-stripping can be started. Using software for that purpose, you will place the disk images sequentially, that is in the correct order.

After placing the disk images in the proper order, adjust the file size, then clone the data to a hard disk. After these steps, the sectors will have been recovered, and the disk will be mountable again.

RAID 3 recovery

In this level, a dedicated parity drive is used to hold the redundancy information, and the data is stripped across the array.

The stripping is done at the byte level. RAID 3 data stripping increases performance, and using a dedicated parity drive takes care of redundancy.

It uses three drives; one is the dedicated drive for parity, and the stripping is done across the remaining two.

Although performance is enhanced, having a dedicated rive for parity slows the drive down.

Every time a write occurs, the parity information for the write has to be written down to the parity drive slowing things down.

To carry out a successful recovery in RAID 3, it will be necessary to find the parity disk, by compressing the image, eliminating it, and then treating it as a stripe. RAID 3 is not used all that much.

RAID 4 recovery

Just like RAID 3, it also has a dedicated parity drive. There are some little changes in its own features though.

For example, in RAID 4, you can change the stripe size, this is done according to application needs, and the stripping is done at block level instead of byte level.

Due to parallelism, RAID 4 performs faster and more efficient read and write operations faster than RAID 3.

This is because it does not have to read all the data across the array, once a single write or read operation is going on.

To do a recovery in RAID 4, you may need to remove the parity disk using the same compression technique, eliminating it, and then treating it as a stripe.

RAID 5 recovery

RAID 5 uses block-level stripping and uses distributed parity. It does use a dedicated parity disk. It has four disks, and the parity blocks are distributed across the disks.

This form of parity distribution means that when a write occurs, the parity data and the data are written across all the disk drives.

Unlike the other RAID levels, this level uses the blocks of data to create the parity blocks, and then they are stored across the array.

It is the most popular of all the RAID levels. Although the parity data are spread across the array or blocks, it still takes time to write them onto the different blocks.

This is because the data and its parity data cannot be written on the same block. Writing the parity to a different block takes time.

Combined with the small calculation that has to take place every time a write occurs, the slowdown that occurs in writes will still exist.

The parity data and the actual data are written onto different disk drives, but never on the same disk. So a data block and its parity data cannot be on the same disk.

This ensures the redundancy and fault tolerance of the array. Once a disk drive is faulty, the array automatically goes into degraded mode. In this mode, the system starts reading and writing the data from the failed drive to the parity blocks on the other disk drives.

The array will be in degraded mode till the faulty disk drive is replaced with a working disk drive.

Once this is done, the data will then be copied back to the new drive, and the array will come out of the degraded mode. RAID 5 uses 4 different disk drives.

The block size can be any size, but it is typically 64kb (128 sectors). The first disk (disk 0) will house sectors 0 through 127, the second disk (disk 1) will include house sectors 128 through 255, disk 2 (second disk) will house sectors 256 through 511, and disk 3 (last disk), and so on. RAID 5 is the most popular of all the RAID levels recovery.

This is because it Offers better availability of data, even when it is running in a degraded mode. The server keeps functioning even when a drive is faulty.

Raid 5 pluses (partial list):

  • Storage efficiency is better – it provides up to 75% if similar drives are used.
  • Fault tolerance is better – it can still run even if one of the drives is faulty. Basically, RAID 5 can function with at least three drives.
  • Its rebuilding is automatic.
  • It offers better random read performance, random write performance, sequential read performance, and sequential write performance.

Complications can occur when an offset is present. When sectors exist before the first striped block, it is called an offset. It can be found by searching for the sector number on the partition table.

After locating the sector number, the disk should be cloned. The cloning should be to a file starting with this sector. This same process should be repeated on all the drives.

After these steps have been taken, try to identify a location on the disk where some patterns occur. You can do this using some software developed for this purpose.

Identify the sector number, then divide this number by the stripe size. Disregard the decimal point (if the result is not an integer). Multiply the integer by the value of the stripe size.

The result is your stripe break point. Once you identify this point, you will notice the difference of data at that point.

In some cases, though, the stripe break point is not that easy to locate, you may have to go through the sectors to be able to locate a break point.

It will be necessary to attentively train your eyes to identify inconsistencies in data as you scroll through the sectors.

If the data is too inconsistent, you may have to go through several areas or portions of the disk to identify the correct stripe break point.

Once the break point is discovered, you can start the RAID 5 de-stripping. Before de-stripping, please be sure to clone all the disks to images on separate disks. Do this twice to be sure. Purchase the original card.

The RAID 5 parity rotation will be the next step in the recovery process. RAID 5 uses any of four algorithms under any operating system to place segments across the array.

Always remember to account for any offset that will cause complications by identifying the partition table and selecting this as your sector 0.

After doing this, you can then use any of the various parity rotation methods to place segments across the array.

Here they are:

  • Left asynchronous or backward parity rotation
  • Left synchronous
  • Right asynchronous or forward parity rotation
  • Right synchronous
  • Backward parity rotation or left-asynchronous

Here the segments are numbered from the first non-parity drive in the stripe to the last drive which is designated as the first parity drive.

The numbering is done sequentially. The selection of the parity drive is done backward and sequentially too, with one drive per stripe.

This is the standard parity rotation method, although some operating systems do not employ this method.

Left synchronous

The segments here are arranged from the extreme left drive and then numbered sequentially from left to right across the array, one drive per stripe. This is a better arrangement for larger reads.

Right synchronous

It is the reverse of the left-asynchronous. The numbering of the segments is still sequential, but it is numbered from the far-most right to the left. The numbering makes sure that only a parity drive is allocated to each stripe.

Right synchronous

It is the reverse of the left synchronous. The sequential numbering is done from the far-most right drive. The numbering is done starting with the next drive in the stripe after the parity.

After doing all this, you will have recovered your drive, and the disk drive should mount.

When a drive fails, the arrays go into what is called a degraded state, or critical state. In this state, the array provides no redundancy as the array is providing data straight from the parity data with no backup.

It is therefore very important to replace failed disk drives as quickly as possible and then rebuild the array.

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