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Extended Self Test vs Surface Scan

PostPosted: 2021.10.03. 12:23
by hoarding__
Yesterday, I bought a new external hard drive, I've already done a surface scan on it and no bad sectors were found! I am currently in a rush, running an extended self test and wondering if I could skip it since the surface test was clean? Is it worth the risk skipping the self test? I mean, aren't these 2 types of scans kinda the same? Any help is much appreciated! :)

Re: Extended Self Test vs Surface Scan

PostPosted: 2021.10.05. 11:01
by hdsentinel
Yes, I can confirm that if you performed the Disk menu -> Surface test -> Read test and it reported no yellow/red blocks, then the disk is fine and yes, you can skip the Extended Self Test.

Generally the Disk menu -> Extended Self Test would also perform a complete surface scan (like the above Read test) EXCEPT that
- the Extended self test may stop immediately on first error
- did not show the speed/performance of the actual sectors

So if you performed the Disk menu -> Surface test -> Read test - then yes, you can skip the Extended Self Test.

Maybe if you want to be 1000000% safe, then you can use the Disk menu -> Short self test too. This is a relatively quick internal self test routine which checks the operation of the drive in general: verify the major components (without performing a complete scan). This quick self test routine is performed by the Extended self test too (just that performs complete surface scan).

So if you do the complete surface scan with the (detailed) Disk menu -> Surface test -> Read test and also you use the Disk menu -> Short self test (and none of them reports problems) then it is completely perfect.

Re: Extended Self Test vs Surface Scan

PostPosted: 2021.12.01. 04:20
by Sibelius
Hmm, I thought for a new disk both Extended test AND Surface Read test were recommended. So are you saying that the Surface Read test already covers everything that the Extended test covers and more? I would like to know since I'm currently running a 31hr Extended test on 2 new 18TB drives, after which I was planning to run the Read test and then the Reinitialization (reference: https://www.hdsentinel.com/faq.php#tests). This is going to take me quite some time and I would want to avoid redundancies. Can you please explain if the Extended test is redundant and if so, why is it listed in step 3 in that link I referenced?

Re: Extended Self Test vs Surface Scan

PostPosted: 2021.12.01. 17:51
by hdsentinel
> So are you saying that the Surface Read test already covers everything that the Extended test covers and more?

Yes, the Disk menu -> Surface test -> Read test is more informative than the Extended self test.
The Extended self test runs inside the hard disk drive and (in addition to checking the functionality of the hard disk drive components in general) performs a surface scan. But it has some limitations, eg. does not report possible slowness plus stops on the first error.

In contrast, the Disk menu -> Surface test -> Read test checks/reports both the status, possible errors and the performance of the disk drive.

On a new hard disk drive (especially on a high capacity hard disk drive) any of the two can be completely fine.
Maybe you can use the Disk menu -> Surface test -> Read test to reveal/confirm the actual transfer speed and have it as a "base" result.
And then, later you can use Disk menu -> Extended self test sometimes, eg. once per month or so, without affecting the current use. It may run for longer time than estimated if the disk drive actively used during the test, so you can use in periods when there is no high disk activity (eg. weekend).


> Can you please explain if the Extended test is redundant and if so, why is it listed in step 3 in that link I referenced?

It is not completely redundant - as each tests performs the surface scan slightly differently.
For example the Surface test -> Read test can show problems (unreadable sectors) when there is a problem with cables, connections, power source or so and these result that sector(s) are not readable. The Extended Self Test runs inside the hard disk, without data transfers, so it can confirm that the hard disk is working correctly in general (regardless of cables/connections).

If there is enough time (usually for a smaller hard disk / SSD), it is ideal to start both of them - but for a very large capacity hard disk, one of them (Extended Self Test vs Read test) is completely enough,
especially if the test result is OK (if the test would show error and/or if the Health would be lower than 100%, then I'd surely check with the other too).

A side note: yes, usually the Reinitialise Disk Surface test is the best way too, but on a such high capacity hard disk it would take VERY LONG time (probably 3-4 days or so).
So you can use the Disk menu -> Surface test -> Write+Read test instead, as this is a "light" version of the Reinitialise Disk Surface (performs less overwrites). It would complete in about half time compared to the Reinitialise Disk Surface test.