Hi Thanh, That is correct. Last time I read the code, Hadoop scheduled the block verifications randomly throughout the period in order to avoid periodic effects (i.e., high load every N minutes).
Brian On Oct 13, 2010, at 7:14 PM, Thanh Do wrote: > Brian, > > When you say *attempt* to complete and *entire* node scan, > you mean for example, if a node has 100 block files, it will > try to verify all 100 block every 3 weeks? > That is in average, a block is scanned every (3 weeks / 100 time interval)? > > Thanks > Thanh > > > On Wed, Oct 13, 2010 at 7:07 PM, Brian Bockelman <bbock...@cse.unl.edu>wrote: > >> Hi Thanh, >> >> The scan period is the period that hadoop *attempts* to complete an entire >> node scan. That is, if it's set to 3 weeks, HDFS will try to scan each >> block once every 3 weeks. >> >> Obviously, depending on the bandwidth you have made available to the >> scanning thread, you can specify impossibly small periods. >> >> Brian >> >> On Oct 13, 2010, at 7:01 PM, Thanh Do wrote: >> >>> Hi again, >>> >>> Could any body explain to me about the scanning period >>> policy of DataBlockScanner? That is who often it wake up >>> and scan a block file. >>> When looking at the code, I found >>> >>> static final long DEFAULT_SCAN_PERIOD_HOURS = 21*24L; // three weeks >>> >>> >>> but definitely it does not wake up and pick a random block >>> to verify every three weeks, right? >>> >>> Thanks a lot, >>> Thanh >> >>
