Question on Performance Counters when Restoring SQL Server 2005 Database

Question

today I do a restore for db of 200G
when the restore start I saw on perfmon that their is only write to the disk
I restore the data files to but no Reading from the source (the same disk).
after 30min of writing in avg of 100MB/sec something to the disk.
The counters on the perfmon change to:
read avg of 50MB/sec
write avg of 50MB/sec
that step take more 1hr, 15min..
I think that everything is OK, buy I don't understand way that happened!

way the first step do a very very short time of reading from the disk (5 sec I think)
and after that the next step was to write only to the disk for a very long time???

Answer 1

updated

backup step 0 (optional): create the MDF and the LDF files, as per the BAK headers description. May result in file initialization (zero out every byte in the newly allocated space). See Misconceptions about instant file initialization .

backup step 1: layout the content of the backup on disk. copies bits from the backup into the .MDF file, then into the .LDF file. Reads from .BAK, Writes to MDF and then to LDF.

backup step 2: run recovery on the database. phase 1 analysis (reads from LDF), phase 2 is redo (reads LDF, writes to MDF) and phase 3 is undo of in-flight transactions (writes to LDF and MDF).