Frequently Asked Questions Concerning Mirrored, Striped, & Other RAID Volumes
Q: What does the term "RAID" stand for?
A: The term RAID is an acronym for a "Redundant Array of Inexpensive Disks" (or a "Redundant Array of Independent Disks"). A RAID set is a collection of disk drives that are grouped together and accessed based on a pre-set configuration to provide data mirroring, striping or redundancy, or some combination thereof. RAID storage systems used to be found only in high-end server applications using SCSI hard drives. Today, manufacturers are building RAID capabilities into the motherboards of many desktop machines using inexpensive, high-capacity PATA and SATA drives.
Q: What is the difference between "hardware" RAID and "software" RAID?
A: Hardware RAID utilizes a special physical controller that maintains information about the hard drives and controls the data write and access functions for the volume. Software RAID (for example, in recent Windows and Mac O/S versions) is an implementation of RAID wherein the normal drive controller is used, and software manages the drives in the array. It can be a less expensive way to implement RAID data storage, but it can be much slower as it places a heavy burden on CPU and memory resources.
Q: How many different levels of RAID are there?
A: RAID levels represent different configurations providing varying amounts of speed and fault tolerance. RAID levels currently defined are RAID 0, 1, 2, 3, 4, 5, 6, 10 (or RAID 1+0), 50 (or RAID 5+0), 100 (or RAID 10+0), and RAID 0+1. The most widely used are RAID levels 0, 1, and 5.
Q: What is meant by the term "JBOD"?
A: "Just a Bunch Of Disks", or JBOD, is not really a RAID configuration. The term refers to hard drives that are concatenated (combined or "spanned") to create a large volume. A JBOD configuration provides no real performance benefits or fault tolerance, but it does allow for total usage of all the available space on each disk.
Q: What is the minimum number of drives needed to create a RAID set?
A: This is determined by the RAID level being used. For example, RAID level 0 (disk striping) and RAID level 1 (disk mirroring) each require at least 2 hard disk drives. A RAID 5 volume, on the other hand, requires a minimum of 3 drives to configure. The storage capacity of the RAID array will be determined by the smallest drive in the array. For example, if three 120GB drives and one 100GB drive are used to create a RAID volume, all four drives will be treated as 100GB drives for purposes of configuring the RAID. Although it is not an absolute requirement, it is always beneficial for optimum performance and storage capacity to use hard drives that are the same make and model when establishing a RAID volume.
Q: I accidently re-formatted my RAID volume(s) - can data still be recovered?
A: In most cases data can still be recovered, but it will depend on how the volume was re-formatted. A re-format through the operating system (Windows, for example) will re-establish the logical volume quickly, but the previous data will still physically reside on the disk. A controller-level format may only overwrite the array information and leave the original data intact (a relatively quick format), or it may overwrite every block on every drive in the array (a considerably longer, low-level process). It depends entirely on the manufacturer of the controller and the format utility used.
Q: Can I run recovery software utilities to recover my RAID volume data?
A: The safest approach to data recovery with a RAID volume (or with any media) is to capture every storage block on each device individually. The resulting drive "images" are then used to help rebuild the original array structure and recover the necessary files and folders. This approach limits continued interaction with the media and helps to preserve the integrity of the original device. One of the dangers in using data recovery software is that it forces the read / write heads to travel repeatedly over areas of the original media which, if physically damaged, could become further damaged and possibly unrecoverable.
Q: If multiple drives fail in a RAID volume all at once, is the data still recoverable?
A: In many cases, the answer is yes. It usually requires that data be recovered from each failed hard drive individually before attempting to address the rest of the volume.
Q: I want Vantage to recover data from a RAID volume - what do I need to send?
A: We only need the original drives that comprised the array. In certain circumstances, it may be beneficial to have the original controller that was being used. However, sending the controller may not be possible or practical, such as when the RAID controller is incorporated into the system motherboard. If the RAID controller is a separate expansion card, it can be included with your shipment of drives for recovery - but it definitely isn't necessary for us to recover the data.
See Also:
Back to Main FAQ
|
