Recently, my desk top PC booted up and performed check-disk more regularly.  After each time the number of used spaces increased and eventually filled up the entire hard drive.
My PC operates with Vista Home Premium with 1T e-SATA hard drive , and the external hard drive is 1T Seagate FreeAgent which is connected to the PC via e-SATA cable.  This disk uses file system NTFS with  4096 bytes in each allocation.  I use this external drive  to store my backup (using Back-Up PROGRAM) and the second copy of my documents from C: (done manually).
During the checkdisk. at the beginning of boot up, the process "recover" all the "orphant" files  and put into a differnt  (new ?) location.  Currently the property shows that  C: drive is "364 GB free of 833 GB; onthe other hand, the external started with <300GB after the first backup and copy.  After each checkdisk, which takes few hours, the used space increased to almost double the previous size then subsequently grows to the whole disk - 931GB.
Here are my questions:
1.   What cause the PC checks disk more regularly lately?
2.   Is there a way to configure the PC only checks disk when I need?
3.   I'm thinking about buying a bigger drive to replace the Seagate.  Although  e-SATA is faster, is it reliable because most of the "well known" brands use USB 2.0? My PC does NOT have USB 3.0.
Thanks for your responses.
Glad to see you are making backups. Good move.

Is the problem mostly or only with the internal drive? Windows does not invoke check disk unless there is some indication of an error.  This feature is not unique to windows, other system has some way to identify errors at star up. Frequent invocation of the check disk indicates something is very wrong. At least one of  two or three things are present:
1.) A Hard drive that has a defect in a critical area of the drive.
2. ) A program that does not close files properly.
3. Part of the OS was damaged by a virus.

Number one is the worst case, because we do not kn ow for sure why the hard drive is doing this. Replacement of the drive may be necessary.

There is no reason to think the external eSATA connection has anything to do with this. We a rte talking about the internal drive.

Of course, there is always the possibility of something else, but I can not even guess as to what it night be. How old is this machine?

Drive diagnostic software is available for the major manufactures. The ones that run off of a boot CD do not require the OS to work. Hi 9PM,

Thank you for your promptness.

Fortunately the problem has been happened only to the EXTERNAL drive; therefore, I do not think about symptoms 2 and 3 of your diagnoses.

Probably I need TWO backup drives Is it practical?

My system is about three years old.

RotorwingHi

yes there is no reason not to have many drives for backup and if you have esata on the computer thats the way to go. When scandisk runs it can create *.chk files which it puts in the root directory. This could be where the free space is GOING.
Sorry I mis understood. I thought you meant the internal drive.
You need to check with Seagate. There have been many stories of problems with external drives. Not just Seagate. And the makers have admitted that are problems. No data has been released to the public, but indications are that the failure rate was so high that many vendors no longer want to sell the items.
It seems the automatic power management of the drives is the main issue. If so, that means you are better off using a simple system the requires manual backups instead of automatic. After a backup is done, turn off the PC and disable the external device. They last a lot longer that way. It would seem that the automatic backup concept has some kind of design flaw.
That is not just my option. There are others who also think auto-backup external drive for a home computer just does not work right.
Don't believe me? Just Google:
"I hate external drives" (no quotes) Quote from: Geek-9pm on October 02, 2011, 12:52:42 AM

You need to check with Seagate. There have been many stories of problems with external drives.

It seems the automatic power management of the drives is the main issue.

Don't believe me? Just Google:
"I hate external drives" (no quotes)

the earth is flat - about 66,700,000 results

The ONLY problems with external drives are:

1) They need to be handled carefully and
2) They aren't designed to be powered on and off daily as internal drives are

I have several external drives, the oldest of which is probably 10 years - and have NEVER had any issues with any of them.

The drives in external enclosures are the same as the ones supplied bare for putting in desktop cases or laptops. They are at no more risk of damage from daily power on/off than internal ones. I guess cheaper enclosures might have a less robust power wart though.

But the user should not have to be a mechanic.

To make a simple analogy, imagine you bought  a brand new bicycle. You use it for a while and the tires are still good. Even the seat does not wear out. The chain is near perfect. But one bad day the the frame falls apart in a heap of broken pieces. Absurd? Yes!

I'm not sure what you've got a bee in your bonnet about. Good quality external hard drives from a reputable maker with a decent warranty are worthwhile products to purchase.

Absurd, and profoundly unlikely.

But users mare finding the hard drives are 'failing' for some odd reason. The failure rates seem to be higher that one would expect. In a number of cases the drives are bad. But  other cases the failure is not from the hard drive itself.

Who says these things? Just you.