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• Standard: optimizes the volume size when combining hard disks with different sizes. if the volume is composed of two or more hard disks, data integrity is protected when one of the hard disks fails.
• Basic: uses only one hard disk to build a volume that does not have any data protection mechanism.
• JBOD: combines at least 2 hard disks to build a volume. Available volume capacity equals to the total capacity of the composed disks. The advantage is it allows combining hard disks with different sizes. The disadvantage is it has worse performance than that of a RAID 0 volume.
• RAID 0: combines at least 2 hard disks to build a volume, which is without any data protection mechanism. When one of the composed disks fails, the data in the volume cannot be rescued. Available volume capacity equals to the total capacity of the composed disks.
• RAID 1: combines 2 – 4 hard disks to build a volume. The system will write identical data to each hard disk at the same time, so data integrity is protected when at least one disk is normal. Available volume capacity equals to the capacity of the smallest hard disk.
• RAID 5: combines at least 3 hard disks to build a volume and stripes both data and parity information across the disks. Therefore, when one of the composed disks fails, the system can be rebuilt by using the parity information on the other disks, so data integrity is protected. Available volume capacity equals to (the capacity of the smallest hard disk) X (number of hard disks – 1)
• RAID 5+Spare: combines at least 4 hard disks to build a volume. It uses 1 disk as the hot spare disk, and the remaining to create a RAID 5 volume. When one of the disks within the RAID 5 volume fails, the hot spare disk will be added to the RAID 5 volume automatically to ensure data integrity. Available volume capacity equals to (the capacity of the smallest hard disk) X (number of hard disks – 2)
• RAID 6: combines at least 4 hard disks to build a volume and stripes both data and parity information across the disks. Therefore, when one or two of the composed disks fails, the system can be rebuilt by using the parity information on the other disks, so data integrity is protected. Available volume capacity equals to (the capacity of the smallest hard disk) X (number of hard disks – 2)
• RAID 10: combines at least 4 hard disks to build a volume, and the number of disks must be even. RAID 10 has the performance of RAID 0 and data protection level of RAID 1. RAID 10 combines two hard disks into a group, in which data integrity is protected when one of the two hard disks fails. Available volume capacity equals to (the capacity of the smallest hard disk) X (number of hard disks / 2)

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RAID 0+1 configuration where multiple disks are striped together into sets (sets A & B in the diagram, each set being as large as the resulting final volume), and then two or more sets are mirrored together.

RAID 1+0 configuration where two or more drives are mirrored together (mirrors 1-4 in the diagram), and then the mirrors (as many as are needed to result in the desired amount of space) are striped together.

In either case (0+1 or 1+0), the loss of a single drive does not result in failure of the RAID system. The difference comes in the chance that the loss of a second drive from the system will result in the failure of the whole system. In RAID 0+1, you have to lose one drive from each disk set to result in the failure of the whole system. In my diagram that would be one drive from set A and one drive from set B. In RAID 1+0, you have to lose all drives in a mirror. This would be both drives in any numbered pair in the diagram.

Mathematically, the difference is that the chance of system failure with two drive failures in a RAID 0+1 system with two sets of drives is (n/2)/(n – 1) where n is the total number of drives in the system. The chance of system failure in a RAID 1+0 system with two drives per mirror is 1/(n – 1). So, using the 8 drive systems shown in the diagrams, the chance that losing a second drive would bring down the RAID system is 4/7 with a RAID 0+1 system and 1/7 with a RAID 1+0 system.

The math gets more complicated when you have more than two elements to a mirror. Since that’s a rare configuration, I haven’t bothered to figure out the equations. If someone else would like to, I’ll be glad to post them here.

Another difference between the two RAID configurations is performance when the system is in a degraded state, i.e. after it has lost one or more drives but has not lost the right combination of drives to completely fail. In a RAID 0+1 configuration, the loss of any drive in a set causes the failure of that entire set and the set is removed from the RAID system. Generally (in the two set case) this means you are left with a RAID 0 system made up of the remaining set of disks. This probably slightly improves write performance and slightly degrades read performance (but that’s just a WAG, I haven’t done any testing). In a RAID 1+0 system, you would see the same effect on each mirror that loses a drive, but not the whole system. In other words, a RAID 1+0 configuration will tend to show similar, but less dramatic, changes in performance when in a degraded mode than RAID 0+1. However, the changes will likely be slight in any case.

One more difference that was recently pointed out to me is the speed at which the RAID system recovers once the failed disk is replaced. RAID 1+0 only has to re-mirror one drive, whereas RAID 0+1 has to re-mirror the entire failed set. So RAID 1+0 will recover significantly faster.

Samsung techies linked 24 of the company’s 256GB SSD drives together in a RAID with the hopes of making the fast SSD drives even faster. The system actually reaches transfer speeds of 2GBps. What’s that much speed mean to you?

• All of Microsoft Office opens in .5 seconds.
• 53 programs from the test rig’s Start menu open in 18 seconds.
• The complete system defrags in about 3 seconds.

INCREDIBLE???

 

Intel’s hot X25-M SSD is one of the faster drives out there, and while it’s not surprising that a RAID 0 array of two of the $600 units is quick, it turns out it’s actually one of the fastest RAID 0 arrays ever. At least that’s the word from the crew at HotHardware, who say that two X25-Ms kicked out the fastest IOMeter numbers they’ve ever seen, and produced 396MB/s reads and 130MB/s writes. Yeah, damn. Anyone going to take the $1200 trip to Speedville?

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