(its gud mrng in India.)
I am unable to understand the following lines by oracle docs.
After 20000 upto 40000 extents extent sets are alaways allocated 8 at a time with the extent size equal to to 4AU.
What My understanding is:
Lets assume I have 4 disks . AU size is 1 mb. Then Extent size are 4AU. I am confused with the allocation of a extent. Whether one extent is allocated in one disk only. Or, it will be allocated to different disk. And If one extent will be allocated to different disk, that means first AU of 4AUs(that is one extent here) will go into disk1,then second AU of 4AUs will go into disk 2 and so on thus allocating one extent in 4 disks. Now since 8 extents are allocated at a time, Rest of the seven extents are also allocated in the same way.
Please let me know whether I am rigth.
In an ASM diskgroup data is striped over the disks with the AU given (default 1MB).
So if you have 4 disks and a tablespace/datafile of 4 MB, the tablespace/datafile will consist of 4 extents, respectively 4 AU. One on each disk.
If your datafile is 4000MB it will consist of 4000 extents (= 4000 AUs) striped over all for disks. So each disk will hold 1000 AUs of the datafile.
This is true up to 20000 extents (respectively 20000 MB).
Now the next extent (20001 MB) for this datafile ASM is allocation will not be a single extent of 1 AU, but ASM will directly allocate 8 extents of the size of 4 AUs.
So for the datafile on disk ASM will have 20008 extents (5002 extents per disk), but since the last 8 extents are 4 AUs, the AU reservered are 20032 AUs or 5008 AUs per disks.
One extent is per disk.
it shows you have given scenario for external redundancy. If taking into account for normal redundancy,if i have 2 failgroups and 2 disk in each failgroups then each disk will contain 2 AUs. That's right?
But now after 2000 extents , 8 extents are allocated at a time. That would means each disk would contain 2 extents among 8 extents. if one extent is allocated per disk then how does striping takes place. First 4AUs will get wriiten in first extent, second 4AU will written in second extent and so on... That's right?
pretty much like the fine grained striping in documentation:
The only thing I could not find is that 8 extends are allocated....
Edited by: Sebastian Solbach (DBA Community) on Aug 9, 2012 12:08 AM