Hopefully the subject of this got your attention, but it's true! I have a file that is 1.2T and it's causing rsync to hang. And as Paul Harvey would say, "now here's the rest of the story..."
I always enjoy his bits...
Further digging reveals that the size of lastlog (not it's physical allocation) is actually equal to the largest user's UID * 292. For some reason, on my system the UID of nfsnobody was set to 4294967294. RHEL4 being a pretty new version, this feels like a bug that hasn't been discovered yet.
I would guess an unintended consequence...
My next check was to see if there is a switch on rsync to have it deal better with sparse files and it turns out if does and SI already uses that switch. I also found the rarely used (at least by me) --sparse=always switch on the cp command. But when I try copying lastlog with that switch, it hangs just like rsyc does. I suspect that both rsycn and cp have to read through the file to figure out which bytes are indeed null and don't need to be actually copied. I do admit that I didn't wait more than a couple of minutes before ^C-ing it
AFAIK, the only way to tell a sparse file, w/o looking at the actual disk allocations, is to see the 0 return from read(20 and know you're not at EOF. So, scanning the file's entire address space is inevitable... I seem to recall some UNIXen would balk on an mmap(2) of the sparse bits, but I forget if Linux is one.
So the bottom line is I'm going to manually exclude /var/log/lastlog when I do my 'getimage', but also felt the need to write this note and at least forewarn people about this situation and see if anyone knows why the UID of 'nfsnobody' is so big.
Because it can be? Seriously, a couple of years ago, people were gritching about 16-bit UIDs, and well, here's the flip side.
-- David N. Lombard Rossmoor, Orange County, CA http://www.fourmilab.ch/cgi-bin/uncgi/Earth?imgsize=320&opt=-z&lat=33.8&ns=North&lon=118.08&ew=West&alt=7&img=learth.evif
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