Dell PowerVault TL2000 - Manual (Page 10)

10
Performance Considerations for Tape Drives and Libraries
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RAID 1
Also known as mirroring, RAID 1 means data is written twice across two disks simultaneously. If
one drive fails, the system switches to the other drive without losing data. During tape drive
backups, the read rate from the RAID 1 array is approximately the same as a single drive because it
is reading from the primary drive. However, restore performance from the tape drive writing to the
RAID 1 array can be slower due to error checking/correction (ECC) included in writing to the
primary and mirrored disks. Much of this inefficiency is due to the fact that the mirroring is often
performed on the CPU or RAID controller. Thus, newer RAID controllers tend to be faster due to
newer and more capable processors.
Figure 1-3. Example RAID 1 Configuration
D1
D2
D3
D4
D5
M1
M2
M3
M4
M5
Tape Drive
SCSI or RAID
Controller
Write Only Read/Write
Read/Write
Hard Drive 1 Hard Drive 2
D = Data Byte
M = Mirrored Byte