rman备份问题，请教！奇怪的问题求解！

iseeku

Directs RMAN to populate each backup set with datafiles from at least integer
disks. This parameter is only enabled when you are backing up datafiles or
control files, and when the operating system can give RMAN disk contention
and node affinity information. To manually disable this feature, set
DISKRATIO = 0.
For example, assume that datafiles are distributed across 10 disks. If the disks
supply data at 10 bytes/second, and if the tape drive requires 50 bytes/second
to keep streaming, then set DISKRATIO = 5 to direct RMAN to include
datafiles from at least 5 disks in each backup set.
If you set FILESPERSET but not DISKRATIO, then DISKRATIO defaults to
the same value as FILESPERSET. If you specify neither parameter, then
DISKRATIO defaults to 4. RMAN compares the DISKRATIO value to the
actual number of devices involved in the backup and uses the lowest value.
For example, if DISKRATIO is 4 and the datafiles are located on three disks,
then RMAN attempts to include datafiles from three disks in each backup set.
The DISKRATIO parameter is easier for datafile backups when the datafiles
are striped or reside on separate disk spindles and you either:
Use a high-bandwidth tape drive that requires several datafiles to be
multiplexed in order to keep the tape drive streaming
Make backups while the database is open and you need to spread the I/O
load across several disk spindles to leave bandwidth for online operations .
Note: Do not spread I/O over more than the minimum number of disks to
keep the tape streaming. Otherwise, you increase restore time for a file
without increasing performance.

iseeku

otn上说的把DISKRATIO = 0就可以了，测试了确实可以，但是不知道是什么原因还是不清楚！
哪位帮忙翻译一下这个

iseeku

otn上说的把DISKRATIO = 0就可以了，测试了确实可以，但是不知道是什么原因还是不清楚！
哪位帮忙翻译一下这个
Directs RMAN to populate each backup set with datafiles from at least integer
disks. This parameter is only enabled when you are backing up datafiles or
control files, and when the operating system can give RMAN disk contention
and node affinity information. To manually disable this feature, set
DISKRATIO = 0.
For example, assume that datafiles are distributed across 10 disks. If the disks
supply data at 10 bytes/second, and if the tape drive requires 50 bytes/second
to keep streaming, then set DISKRATIO = 5 to direct RMAN to include
datafiles from at least 5 disks in each backup set.
If you set FILESPERSET but not DISKRATIO, then DISKRATIO defaults to
the same value as FILESPERSET. If you specify neither parameter, then
DISKRATIO defaults to 4. RMAN compares the DISKRATIO value to the
actual number of devices involved in the backup and uses the lowest value.
For example, if DISKRATIO is 4 and the datafiles are located on three disks,
then RMAN attempts to include datafiles from three disks in each backup set.
The DISKRATIO parameter is easier for datafile backups when the datafiles
are striped or reside on separate disk spindles and you either:
Use a high-bandwidth tape drive that requires several datafiles to be
multiplexed in order to keep the tape drive streaming
Make backups while the database is open and you need to spread the I/O
load across several disk spindles to leave bandwidth for online operations .
Note: Do not spread I/O over more than the minimum number of disks to
keep the tape streaming. Otherwise, you increase restore time for a file
without increasing performance.