First page Back Continue Last page Graphics
Tape Buffer / Block Size
For tape backup, RMAN allocates
- 4 buffers per channel
- Usually 256KB
- In large pool if async IO, else PGA
Increasing tape buffer size might help
Increase physical tape block size to match buffer size
- That’s done on the MM side, e.g. Veritas
Notes:
Increasing the tape buffer size can help keep a tape device streaming – so if your device is doing lots of starts and stops, this could help (so could increasing the level of multiplexing).
The Oracle manual recommends setting BLKSIZE to “a little less” than the block size of the tape. (See chapter 14 of the Oracle9i Recovery Manager User’s Guide for more information. ) However, note the following error I received when the block size was not a multiple of the physical block size:
RMAN> run { allocate channel t1 type sbt MAXOPENFILES 1
2> PARMS="BLKSIZE=1000000";
3> backup force tag='pgatest' tablespace ts5; }
RMAN-00571: ==================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ====
RMAN-00571: =================================================
RMAN-03009: failure of allocate command on t1 channel at 11/29/2003
ORA-19554: error allocating device, device type: SBT_TAPE, device na
ORA-27018: BLKSIZE is not a multiple of the minimum physical block size
Additional information: 1000000
Additional information: 16384
Note that adjusting the tape buffer size did not help in my environment (I tested 512K and 1M buffers). That could have been because the media manager in use – Legato LSSV – did not allow me to adjust the physical tape block size.