SFW Mirroring vs RAID

I am looking for any thoughts on the pros & cons of using software disk mirroring versus a hardware RAID solution as the disk subsystem for a large Oracle server. I'm mostly interested in the performance and control of Oracle from a DBA's perspective. The environment is Oracle 7.0 under an HP Series 800 machine. I am using file-system disk only (no Unix raw partitions).

In general, I would like to get any feedback on what people are doing and/or where they are going in this area.  

This is what I've gathered so far:

Software Mirroring

Advantages:
- traditional method for doing disk high availability

• higher level of fault tolerance (duplicate disk controller, cables, etc.)
• complete control of database file placement, ie which physical disks will maintain DBMS logs/tables

Disadvantages:
- high cost; requires 100% duplication of disks & controllers

Hardware RAID

Advantages:
- lower cost; typically requires only 20% disk overhead for RAID 5

• no thought process required for database table placement. ie rely on hardware stripping to spread disk I/O across disks

Disadvantages:
- lack of control for what disks are assigned to what
  database tables/logs.
- SCSI controller & cable represent single point of failure.
 

Thanks in advance.

Dave Roberts

EDS Canada

robertsd_at_bbs.ug.eds.com
ph (905)644-5779
fx (905)644-3936 Received on Tue Aug 30 1994 - 13:20:07 CEST