Slow boot after Mavericks

Question

Hello guys.
Like many of Mavericks's user, I'm experiencing some problems in OS boot, such as slow boot or even a freeze, that I've never experienced before. I've read a post that someone teaching how to show errors, if there is any, by typing this code line into Terminal:
syslog -k Sender kernel -k Message CReq 'Channel t|GPU D|I/O|find tok|n Cause: -' | tail | open -ef
After typing that this error has appeared into the TextEdit: Dec  1 20:48:50 b12058e8 kernel[0] <Debug>: disk0s2: I/O error.
Does anybody knows what it means? It indicates a possible problem in my HDD?
My computer is a:
MACBOOK PRO
15-inch, Late 2011
Processor  2.2 GHz Intel Core i7
Memory  8 GB 1333 MHz DDR3
Graphics  Intel HD Graphics 3000 512 MB
Serial Number  C0*******V7L
Software  OS X 10.9 (13A603)
Thanks
<Personal Information Edited by Host>

Answer 1

The disk drive may be corrupted or has failed. Backup all your files, then try this:
Install or Reinstall Mavericks, Lion/Mountain Lion from Scratch
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Erase the hard drive:
  1. Select Disk Utility from the main menu and click on the Continue button.
  2. After DU loads select your startup volume (usually Macintosh HD) from the
      left side list. Click on the Erase tab in the DU main window.
  3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on
      the Security button and set the Zero Data option to one-pass. Click on
      the Erase button and wait until the process has completed.
  4. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion, Mavericks: Select Reinstall Lion/Mountain Lion, Mavericks and click on the Install button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible
            because it is three times faster than wireless.