Log and Data on the same RAID?

Maybe my question is too simple because I dont know much of RAID,
but I try:
What is probably "better": One RAID of 4 Disks, where datafile and logfile are
placed on, or Two RAIDs of each 2 Disks, where one RAID contains the datafile
and the other RAID contains the logfile?
JoachimAs all questions related to computers, the correct response is 'It depends'.
A mirror RAID drive would be good for the log file, a mirrored drive for the
datafile is less than optimal. If you only had 5 drives, you could mirror
the drive for the log and create a RAID 5 for the datafiles.
If have to work with only 4 drives, additional informational needs would
include: type of database (OLTP/OLAP), Number of users, amount of traffic,
concurrency of traffic, average size of queries, amount of INSERT/UPDATE
traffic, etc.
--
Arnie Rowland, Ph.D.
Westwood Consulting, Inc
Most good judgment comes from experience.
Most experience comes from bad judgment.
- Anonymous
"Joachim Hofmann" <speicher@.freenet.de> wrote in message
news:4l8o3aFpta8U1@.individual.net...
> Maybe my question is too simple because I dont know much of RAID,
> but I try:
> What is probably "better": One RAID of 4 Disks, where datafile and logfile
> are
> placed on, or Two RAIDs of each 2 Disks, where one RAID contains the
> datafile
> and the other RAID contains the logfile?
> Joachim|||It depends on a lot of things but the biggest of which is how many reads to
writes you do. If you have mostly read only operations you may get better
read results by having a 4 disk Raid 10. If you have a lot of writes you may
need to separate the log file from the data files. If you only have 4 disks
you have little choice but to use two Raid 1's.
--
Andrew J. Kelly SQL MVP
"Joachim Hofmann" <speicher@.freenet.de> wrote in message
news:4l8o3aFpta8U1@.individual.net...
> Maybe my question is too simple because I dont know much of RAID,
> but I try:
> What is probably "better": One RAID of 4 Disks, where datafile and logfile
> are
> placed on, or Two RAIDs of each 2 Disks, where one RAID contains the
> datafile
> and the other RAID contains the logfile?
> Joachim|||I would add to that, IF the RAID array controller is suitable for
write caching (battery backed memory on the controller and other wise
certified for that sort of thing), then the write penalty for RAID5 is
somewhat minimized.
Roy Harvey
Beacon Falls, CT
On Fri, 25 Aug 2006 10:25:44 -0700, "Arnie Rowland" <arnie@.1568.com>
wrote:
>As all questions related to computers, the correct response is 'It depends'.
>A mirror RAID drive would be good for the log file, a mirrored drive for the
>datafile is less than optimal. If you only had 5 drives, you could mirror
>the drive for the log and create a RAID 5 for the datafiles.
>If have to work with only 4 drives, additional informational needs would
>include: type of database (OLTP/OLAP), Number of users, amount of traffic,
>concurrency of traffic, average size of queries, amount of INSERT/UPDATE
>traffic, etc.