WHM backup can't fine the "mysql" directory

Hi all,

I am having a very busy LAMP server with 4 accounts.
After I download WHM full cron backup XXX.tar.gz and decompress it, three of them backup are normal, but the other account with about 2 GBs of database and 6GBs files, After this big.tar.gz decompressed always can't fine "mysql" directory.

Its very strange, that if I decrease my website some files and keep the big.tar.gz below 8GBs, then I finally can fine the mysql backup.

Can anyone help me please..........

Server configuration is Intel(R) Core(TM)2 Quad CPU Q9550 @ 2.83GHz, & 8 GB of RAM.

Thanks...