Linux (& Samba) is good enough
It sounds like you've got major HW issues, so you need to fix those first.
I recommend you read up on http://linux.die.net/man/8/smartctl
. These tools run low level disk checks (whilst they're running) and warn you about disks likely to die soon.
BTW, I believe this is just for individual disks; for HW RAID you'll need to get the manufacturers diagnostics tools.
If the network is truly saturated you may have to persuade your management to up grade eg 10G => 100G, but I'd definitely start by checking all cables/cxns and replacing where needed.
Bad network hw will kill the the throughput, regardless.
I highly recommend you document all the fixes/replacements you do in case you need to get some money out of management later.
Can you confirm which distros+versions of Linux you have
If you're relatively new to Linux, here are some good links
- good cmd line tutorial
- a lot(!) of free to read books/manuals; you may want to start with the SysAdmin section
Good Luck & Welcome to LQ