Why would full format run hugely faster than chkdsk /r?

Rick441

Distinguished
Apr 10, 2011
24
0
18,520
Last week I ran a chkdsk /r on a half-full, single partition 3.5-inch 500gb 7200rpm external hard drive (32mb cache), and it took 4 or 5 hours to complete. No problems were found. Today I ran a full format on new, single-partition 2.5-inch 500gb 7200rpm external drive (16mb cache), and it only took about 20 minutes. Any idea why there would be such a huge completion-time discrepancy? My understanding was that full format looks for bad sectors just like (the time-consuming part of) chkdsk /r. I’m using Windows XP-SP3, and both drives are in external enclosures connected by USB 2.0. They seem to have similar file transfer rates. Thanks.
 
Solution
i see, but as kenrivers explained " full format, which only checks for bad sectors " while chkdsk /r actually check sector by sector and tries to recover that bad sector. format doesn't it just marked them.
chkdsk /r not only "looks for bad sectors" but also check the file( cross-linked. etc),sector of your drive and try to recover them
whereas format only care about overwriting the current format and if does find a bad sector it just marked them.
 

Rick441

Distinguished
Apr 10, 2011
24
0
18,520


But aren't the surface scans (to identify bad sectors) a separate phase from the much-quicker-running file system checks (e.g. for cross-linked files)?

 
chkdsk /f only checks for drive errors and not bad sectors
chkdsk /r implies that chkdsk /f is run and checks for bad sectors on the disk and recovers any readable information
In other words chkdsk /r checks both files and does a surface scan. This may explain why a full format, which only checks for bad sectors, does not take as long as running chkdsk /r. I think this is exactly what qazzi was stating.
 

Rick441

Distinguished
Apr 10, 2011
24
0
18,520
Maybe I wasn't making it clear, but the stage of the chkdsk that does the surface scan (stage 4, the stage invoked by the /r switch) is what accounted for almost 100% of the 4-5 hours with the half-full drive. The other stages, e.g. looking for file-system error, flew by and contributed virtually no time to the scan. So -- unless I'm failing to understand something -- the file-system checks can't account for the huge time discrepancy between chkdsk /r on the half-full drive (again, with zero errors of any kind) and the full format on the new drive.