The term RAID often applied to RAID level 0 or JBOD doesn't explain the actual functions. These storage types perform in the following way:
JBOD: storage extended with some number of disks even of different sizes. Each component of JBOD follows the previous one to create a solid storage with the size equal to the sum of the sizes of each component. JBOD is supported by most hardware RAID chips as well as software RAID (e.g. Dynamic Disks under Windows can span among different disks or disk partitions).
RAID0: stripe set on disks of equal size. Data on RAID0 are divided into 'stripes' of equal size and are cyclically distributed among all disks. Such 'stripe' size usually ranges from 512 bytes and up to 256KB. Data striping technique serves to distribute long data fragments among all disks. This allows to issue data exchange requests to all drives simultaneously and to speeding-up this action with parallel read or write. These systems feature the highest speed of operation and maximally efficient use of disk space.
Data recovery chances for these systems are obvious: even if one single disk from this RAID cannot read, data from this component become unrecoverable. If failure of a single disk occurs on JBOD, the entire fragment of span becomes unrecoverable. For RAID0 this will affect all data on RAID (e.g. if RAID0 is built on 4 disks with stripe size 16KB, after failure of a single disk RAID will have 16KB 'hole' after each 48KB block. In general, this would mean any file with size over 48KB can not be recovered).
Note: If one or more disks from RAID0 or JBOD failed - the disk use should be immediately stopped and bring it to data recovery laboratory. Only physical drive repair can help to recover the data in this case.
If the reason for a RAID failure is other than failure of a single disk (e.g. re-set of controller settings, failure or damage of controller etc.) data remain recoverable even after logical damage of a file system. The only thing you should do in this case is to assemble the original solid storage using data recovery software. For this you have to note the disks included into RAID, initial drive order and stripe size for RAID. Data recovery software will read data from components in the same manner as RAID controller does and will access files completely on virtually reconstructed RAID.
Mirror technique is implemented in RAID1. Data of each of RAID components are duplicated enabling recovery of lost information from any undamaged component of the RAID-system. In mirror RAID the controller performs parallel reading operations to speed-up read access to files.
Advanced redundant systems
This kind of storage features the highest redundancy and the best chances for data recovery. The only action you should do is to scan the storage once using efficient data recovery software.
Advanced redundant systems are created to compromise between high speed of storage access, storage size and redundancy. These systems usually are based on the idea of striping from RAID0, but storage data are extended with extra information (parity information) adding redundancy and allows users to recover data or even continue work with the RAID storage after a failure of its component.
Such systems include RAID3, RAID4 or RAID7 (stripe set with dedicated parity), RAID5 (stripe set with distributed parity) and RAID6 (stripe set with double distributed parity). The term 'single' parity means that the data are recoverable or the system is operative after failure of a single component; 'double' parity - after up to two components.
RAID3 and similar systems use classic technique of RAID0, extended with one additional disk to store parity. RAID5 and RAID6 distribute parity among all disks to speed-up parity update process for data write operations.
Data recovery from these systems is possible for completely undamaged RAID, as well as if one (for RAID3, RAID4, RAID5, RAID7) or up to two (for RAID6) components remain unreadable.
Note: If more disks fail than permitted, stop using the storage immediately and take it to a data recovery laboratory. Recovering the data is only possible with repair.
If data recovery is possible without repair, you should assemble your RAID using data recovery software specifying the drives (including placeholders for any missing drive), drives order, stripe size and parity distribution algorithm. Data recovery software will read the data from RAID components in the same manner as RAID controller does and will access files completely on virtually reconstructed RAID.
RAID-on-RAID configurations are often used to improve overall performance, add redundancy and for other performance - related reasons. Usually such systems are combinations of RAID systems mentioned above. The most classic are systems like RAID10: several 'mirrors' with 'stripe' over them. Mirrors here ensure redundancy and stripe over mirrors adds read/write speed. Data recovery from such system is quite simple: you should take any undamaged component from each mirror and virtually build RAID0 over it.
More advanced systems include RAID50 (stripe over RAID5), RAID51 (mirror of RAID5) etc. To reconstruct such system building each component of RAID (in this example each RAID5) and building RAID0 for RAID50 over the set of RAID5 is required.
We recommend UFS Explorer RAID Recovery as the most efficient software for data recovery and virtual reconstruction of any RAID level.