Specifications

5-2
VENICE 2U/Element Hardware Guide
5.1 Hard Disk Maintenance
This section deals with the possible event of a hard disk failure. First,
some introductory information about RAID are provided. After that fol-
low descriptions how to act when a hard disk fails.
5.1.1 Introduction to RAID
In a system where huge amounts of data are processed, large storage
capacities combined with high data throughputs are mandatory. To
provide both at the same time it is common practice in the area of video
and digital film to configure several hard disks together into a stripe set
or RAID. The IT world has defined several ’levels’ of RAID, most of them
providing some kind of data protection.
The RAID feature makes the DVS system tolerant of disk failures. Even
with a broken disk operations can still be continued and, once the failed
disk has been replaced, the missing data can be recovered easily. The
data protection is provided by a RAID controller installed inside the sys-
tem which independently administers the data protection for the sets
of hard disks connected to it.
The system/metadata hard disks are protected by a RAID 1 applied to
the data, meaning by a mirroring of the data between two disks. If one
of the hard disks fails, the missing data can be restored with the mir-
rored information stored on the other disk.
The main storage of the DVS system comprises up to 10 hard disks that
are protected by a RAID 6 applied to the data. With this, the data is
striped across these hard disks during write procedures. At the same
time the information necessary to rebuild a failed hard disk (parity infor-
mation) is generated and written across the disks as well. Because
RAID 6 writes the parity information twice to different hard disks (dual
parity), up to two hard disks can fail and your data will still be recover-
able due to the information stored on the other disks. Especially server
systems make use of the RAID 6 feature because, particularly with larg-
er disk capacities, the recovery of a single disk can take a long time and
the failure of a second disk in the meantime is not unlikely anymore.
The following figure shows a representation of the hard disk array of the
DVS system (see also section “Hard Disk Array” on page 2-7). It indi-
cates the location of the disk sets (RAID packs) in the hard disk array:
If the second disk fails in the meantime, the data will be unre-
coverable.
If a third disk fails in the meantime, the data will be unrecov-
erable.