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Appendix
Lifetime of Hard Disk
A hard disk is a storage device that works physically, and has a limited lifetime. It is a kind
of consumables. It is said that the average lifetime of a RAID system composed of SCSI
hard disks is three years. However, this lifetime is considered to be true for standard file
servers or business servers. The disk failure rate of VK-64/VK-16 systems is higher than
that of general file servers. It is reasonable to assume that the lifetime of hard disks in a
VK-64/VK-16 system is about half of that of a standard file server (one and a half years).
Therefore, when you build a VK-64/VK-16 system, it is advisable to provide a hot-spare
(spare hard disks that are active) for RAID configuration.
RAID Reconfiguration
If one of hard disks in RAID1 and RAID5 systems breaks down, you can restore the
system by replacing the broken hard disk before other disks break.
Restoring the data stored on the broken hard disk after replacement is referred to as
rebuilding.
During RAID rebuilding, a recording error may occur because disk system performance
deteriorates.
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RAID Rebuilding Time
When a failure occurs in a hard disk in a RAID system and you want to replace it with a
hot-spare or new one, the rebuilding time is to be considered as follows:
Rebuilding takes about one minute per 1GB when no I/O is performed in a SCSI RAID
card.
When a RAID system is composed of four SCSI hard disks of 300GB each, the total
disk size of the hard disks is 1200GB. To rebuild this system, 1200 minutes (20 hours)
are required on the condition that there no I/O is performed.
If rebuilding takes 20 hours when there is no I/O, the rebuilding time for a VK-64/VK-16
system where I/O is continuously performed can be assumed to be about 20 x 2 hours.
Thus, when you perform rebuilding without stopping recording, it takes about 40 hours.
There is no problem if rebuilding only takes a long time. However, the other hard disks
may break down one after another during such rebuilding. If another hard disk breaks
down during rebuilding, all of the stored data will be lost. Therefore, it is preferable to
reduce rebuilding time as far as possible.
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