Case Studies
Case Study 1: Typical RAID- 5 data recovery after multiple fragment failure
styles to recover data from a RAID- 5 Array
RAID – spare Array of Inexpensive Disks is used to give increased storehouse reliability and lower time-out. The two most common perpetration of RAID that Precision Computers receives for recovery is RAID 1( glass) and RAID 5( distributed equality). Put utmost simply in the case of a RAID1 or RAID5 there's spare capacity within the storehouse array to allow for a single fragment failure.
RAID 5 data loss
generally we find that the main cause for data loss in a RAID 5 array is multiple fragment failures. In our experience, it's lower frequent for disks( HDD or SSD) to fail contemporaneously. generally there has been a single fragment failure, days, weeks, or months prior to the alternate fragment failure. Unfortunately, during this period the system director has either not noticed, or indeed neglected to replace the first failed fragment. also a alternate fragment failure occurs performing in the failure of the RAID. constantly the system director is ignorant in which order the disks have failed.
Establishing the order of failure
Where ever possible it's necessary to produce a full fragment image of each fragment in the RAID set. Not only does this insure that the data is stored safely and minimise the chance of an fresh fragment failure, but it allows for the effective comparison of data across the fragment set. This work is conducted first as per our standard single- fragment recovery styles. Once fragment images have been created it's necessary to compare the data structures across these. If we've access to all the disks in the RAID set also it's possible to run an XOR evaluation to test whether data is harmonious across the RAID array. This will give some suggestion of whether one fragment has failed occasionally before a alternate.
Understanding RAID 5 and XOR
RAID 5 uses a bitwise “ exclusive OR ”( XOR) function to cipher the equality values from the array data. The XOR function satisfies two important conditions still, also X = Z XOR Y, and also Y = Z XOR X, If X XOR Y = Z. Still, Z also occupies that number of bits, If X and Y enthral the same number of bits. X XOR Y = Z X Y Z 0 0 0 1 0 1 0 1 1 1 1 0 Using these parcels of the XOR function allows one to calculate one of the missing values given all the others.
Hexadecimal Editor examination
XOR tests will show if there's good thickness across the fragment set. It'll not tell us which fragment is inconsistent. This must be done by the technician working on the RAID array.
Case Study 2: Notebook disk goes clunk
When a divisional sales manager's notebook disk made a worrying 'clunk' noise, she realised that she had lost all data relating to an important multi-million tender. To make matters worse, the out-of-office work had not been backed up. With the deadline just over a week away, the company's IT manager contacted us in a panic.
We quickly located and repaired the faulty read/write heads in the platter chamber, created a construct/analogue of the disk, repaired any faulty partition tables, and recovered the required data.