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There are many RAID systems on the market.  They can often be a small box with 2-8 drives in it, often used as a NAS (Network Attached Storage) device.  Many of these systems actually contain a processor and a Linux operating system, which then controls a RAID 5 controller.  To make the system slightly more complex for recovery, the disk may be in multiple partitions, so that Linux can be booted, and then a large partition where user data can be stored.  From the host PC, the NAS just looks like a logical drive, that will store files.  The host has no knowledge of how files are stored, which could actually be using any file system, though XFS does seem fairly common on new devices.

To determine the layout of a RAID is not trivial as it requires knowledge of file systems, and RAID structure.  The following parameters have to be determined

• Stripe size
• Stripe configuration
• RAID start location.

Stripes

The stripe size is often the easiest to work out by hand.  It is easiest to locate a long text file and it will then be clear when the text is not contiguous (allowing for file fragmentation).  Typical stripe sizes are 0x80 and 0x100 sectors, though this can range from maybe 0x8 to 0x4000.

Configuration

The stripe configuration can be very difficult unless again there are some long, unfragmented text files.  With a text file it is often easy to confirm that data is correct over a stripe boundary.  Trial and error may be required and the following patterns may be seen for a 4 drive RAID 5

       1  2  3  P                P   1   2   3                1   2   3   P

       4  5  P  6                4   P   5   6                5   6   P   4

       7  P  8  9                7   8   P   9                9   P   7   8

       P 10 11 12                10 11 12  P                10 11 12  P

If the selected pattern is wrong, so will the data

RAID start location

Not all RAIDs are the same through the whole area of the disk.  A common exception is to store the Linux operating systems files on all disks, ie as a RAID 1 configuration.  The RAID 5 will then start at a location later on the disk.  To implement this feature, the RAID1 can be ignored, and the RAID can be set to start at a defined location.

Preconfigured RAID setups

To assist with reading proprietary RAIDs,  certain settups will be distributed with the software.  This will be if nothing else a basis for configuration, and any parameter may be changed.