Using PDM, the time to migrate data from a 'sick' drive to a healthy one is up to five times faster than a traditional RAID 5
In RAID 5, data is cut into fixed-size strips and separately stored in the hard disks in turn; meanwhile, a parity block will be created in each horizontal stripe or block and is designed to protect other data blocks in horizontal blocks, but can only handle single data block damage.
Following figure illustrates how the shadow section is created in the process of disk array recovery in the RAID 5 composed of 4 hard disks:
Today's RAID storage solutions provide either limited protection (RAID 5), prohibitive expensive (RAID 5+1) or both (RAID 1+0).
With RAID[.sup.n], companies achieve greater protection than RAID 1 or RAID 5 simply by configuring one extra drive.
Again, as seen by Figure 1, there is a big jump in reliability between RAID 5 and RAID ADG.
And with the 40% faster I/O times, the system would be able to achieve faster I/Os then the 60 10,000-RPM (76GB) hard drive solutions using standard RAID 5.
In addition, the total amount of data at risk has also doubled every year, now that the RAID 5
array may actually contain every piece of data the company owns.
To reduce downtime due to component failures, there are three different methods to mirror your RAID 5
storage systems to provide a cost-effective solution for protecting critical situations.
RAID 3 and RAID 5
each use one extra disk to store parity information needed to recreate data in the event of a single disk failure.
To perform a write operation to a RAID 5
disk array, it is necessary to perform what is normally referred to as a "Read-Modify-Writeback" operation.
The unit supports RAID 5
with hot spare capability and ships with redundant power supplies as standard features.
Since RAID 5
is essentially a performance-enhanced variant of this RAID level, RAID 4 has been displaced in market.
Disk arrays based on RAID controllers using CPU-based XOR calculations normally perform RAID 5
writes in the 5MB/sec-l5MB/sec range.
Fibre Channel storage is not well suited for most business applications, since FC-AL arrays usually require the host to perform RAID 5
. Using any host-based RAID 5
is unacceptable to most users of high performance servers, since reliability and performance are dramatically reduced over hardware RAID 5