I have 2 sata discs.
-- sata1 which is formatted with NTFS
-- sata2 (not mine) which is unformatted empty and bigger than sata1.

I borrowed the sata2 from a friend so that I can move the whole contends of sata1 to sata2 so that I can format sata1 to ext3 and move back the data from sata2 to sata1 and get rid once and for all the damn NTFS since I finally got rid of M$ Windows.

The amount of data is ~ 170GB and so as you understand it is crucial to get the job done corretly.
So if you know the correct and safest way (not fastest) to do it and also done it a few times yourself please decribe the way if you can.
Please feal free to write some examples if you can.

I can't use cp because i'll get out of memory and out of swap.

"I can't use cp because i'll get out of memory and out of swap."

I've never had this happen to me. Do you have some unusually large files on sata1? You could partition sata2 with a large swap partition leaving enough room to accept the data from sata1 with a little to spare.

Unless you have a ridiculously small amount of memory and swap, using cp should be fine. It doesn't store the whole thing in memory before writing it out, but rather, it will read a N-byte block, then write the N-byte block to the other drive, then repeat for the next block. N varies depending on your cp version, IIRC. I think it is on the order of 4-16k.

I have a lot of big files (700+MB) but I don't like cp.
I have 1GB or RAM for now.
I was thinking of a way with tar or dd.

Well, I suppose you could do:
Is there a reason you don't like cp? I copied ~120GB a couple of weeks ago using cp with no problems: and no swap enabled. (And much of my memory was used, running from a LiveCD)