User guide

2–6 Hardware architecture
Hitachi Unified Storage VM Block Module Hardware User Guide
Item Description
Description Data is written to multiple disks successively in units of block
(orblocks). Parity data is generated from data of multiple blocks and
written to optional disk.
Advantage RAID 5 fits the transaction operation mainly uses small size random
access because each disk can receive I/O instructions independently.
It can provide high reliability and usability at a comparatively low cost
by virtue of the parity data.
Disadvantage Write penalty of RAID 5 is larger than that of RAID 1 because pre-
update data and pre-update parity data must be read internally
because the parity data is updated when data is updated.