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New technology makes RAID5 acceptable for Oracle
databases
Oracle Database Tips by Donald Burleson |
Disk vendors have been at-odds with Oracle for many years, as most
disk vendors offer RAID5, a RAID level that minimizes wasted storage,
but has a high update penalty.
Oracle 10g has adopted the RAID10 standard as SAME (Stripe and Mirror
Everywhere) within their popular Automatic Storage Management (ASM), but the
technology is changing and some storage vendors have overcome the infamous
"write penalty" that has been traditionally associated with RAID5 on Oracle.
Vendors address changing Oracle storage
demands
As the technology changes, storage vendors are making great strides,
especially in the areas of Solid State Disk and specialized RAID5 doe databases:
Super-fast access with solid-state Disk:
http://www.texmemsys.com/files/f000139.pdf
High-speed RAID5 for Oracle:
http://www.vion.com/GSA%20PDFs/16-TagmaStore%20HW%20-%20Maint.pdf
The next generation of RAID5 for Oracle
One great area of RAID5 is that it's commonly used by all of the major disk
vendors and it has less storage overhead than full disk mirroring.
In 2006, many disk vendors have made advances that overcome the "write
penalty" associated with high update activity and there are now RAID5
storage devices that can accommodate high update databases without the
high "write penalty" latency.
One such product is the
Hitachi TagmaStore
RAID5 "Universal Storage Platform". In a nutshell, the TagmaStore
device uses a large 256GB cache to overcome the RAID5 write penalty.
Because this cache is so huge, the database can write to disk and move
on; the parity is calculated from the data in cache asynchronously. So
unless the cache is over-extended, the database will not suffer the RAID
5 write penalty.
The TagmaStore documentation notes that it the sophisticated cache that
makes allow the benefits of RAID5, but without the update penalty:
"Cache memory is memory used to perform
data read/write processing efficiently between front-end and back-end
directors. The cache capacity on both sides is configured to be a minimum of
4GB, to a maximum of 256GB, with expansion in units of 4GB or 8GB.
The disk controller performs control so
that there is always the most efficient use of the cache in response to data
access patterns, thus obtaining a highly stable level of performance.
As an optional expansion, access paths to the cache can be doubled to obtain
internal data trans-mission capacities in combination with a cache switch
for a maximum of 68GB/sec."
Oracle RAID5 References:
and include the URL for the page.
