February 11, 2006

Oracle & RAID

Writing about web page http://asktom.oracle.com/pls/ask/f?p=4950:8:2921391741443371367::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:359617936136

  • One very good point is multiplexing online log and control file even you are using RAID 0+1 (stripe & mirror)
  • RAID 0+1 for undo space since it cannot be multiplexed, read/write frequently
  • RAID 5 or 0+1 for datafile,

The result of df -h on our serve:
is every entry a paired disk?
If not, how to check, fdisk?

The relationship of controller and disk, 1 to 1 ?
the IO speed decided by controller , I guess ? Then how controller interact with the disks?

Also see: link

0+1 and 1+0 have same performance. 1+0 has better availability.
What we use then ?

RAID 0: no reliability; improve performance
RAID 1: provides the highest performance for redundant storage
RAID 2: No implementation
RAID 3: Not good for database
RAID 4: Performance no better than 5
RAID 5: Parity RAID allows redundancy with less total storage cost. The loss of a single disk will cause read performance to be degraded while the system reads all other disks in the array and recomputes the missing data.

- 2 comments by 2 or more people Not publicly viewable

  1. Chris May

    Hmm; the idea of using different RAID configurations for different parts of the DB is smart, but it seems to assume you've got a lot of disks to play with! If you've only got 2 or 4 disks (as is the case in most of our midrange boxes) then you've really got to pick one configuration and go with it.

    12 Feb 2006, 10:09

  2. Steve Rumsby

    If you want good performance from Oracle databases, though, you really do need lots of spindles. You put the online redo logs on two spindles of their own, the archive logs on another, and all of those separate from the data files. And then the paranoid amongst us mirror everything, even if we have oracle mirroring of the redo logs. That's a lot of spindles, and a lot of wasted space with today's huge disks. But that's what you need to do. At least, that used to be the advice in years gone by.

    These days, people seem happy with the idea of putting everything together in one lump, provided though that it is spread across a RAID group with lots of spindles. So, still lots of spindles required, but more efficient use of of capacity.

    13 Feb 2006, 11:28

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