We have a small "homemade" server running fully updated Debian Wheezy (amd64). One hard drive installed: WDC WD6400AAKS. The motherboard is ASUS M4N68T V2.

The usual load:

• CPU: an average of 20%
• Each week about 50GB of additional space is occupied. About 47GB of uploaded files and 3GB of MySQL data.

I'm afraid that the hard drive may be about to fail. I saw Pre-fail on few places when I ran:

root@SERVER:/tmp# smartctl -a /dev/sda
smartctl 5.41 2011-06-09 r3365 [x86_64-linux-3.2.0-4-amd64] (local build)
Copyright (C) 2002-11 by Bruce Allen, http://smartmontools.sourceforge.net

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital Caviar Blue Serial ATA
Device Model:     WDC WD6400AAKS-XXXXXXX
Serial Number:    WD-XXXXXXXXXXXXXXXXXXX
LU WWN Device Id: 5 0014ee XXXXXXXXXXXXX
Firmware Version: 01.03B01
User Capacity:    640,135,028,736 bytes [640 GB]
Sector Size:      512 bytes logical/physical
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   8
ATA Standard is:  Exact ATA specification draft version not indicated
Local Time is:    Mon Oct 28 18:55:27 2013 UTC
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status:  (0x85) Offline data collection activity
                    was aborted by an interrupting command from host.
                    Auto Offline Data Collection: Enabled.
Self-test execution status:      ( 247) Self-test routine in progress...
                    70% of test remaining.
Total time to complete Offline 
data collection:        (11580) seconds.
Offline data collection
capabilities:            (0x7b) SMART execute Offline immediate.
                    Auto Offline data collection on/off support.
                    Suspend Offline collection upon new
                    command.
                    Offline surface scan supported.
                    Self-test supported.
                    Conveyance Self-test supported.
                    Selective Self-test supported.
SMART capabilities:            (0x0003) Saves SMART data before entering
                    power-saving mode.
                    Supports SMART auto save timer.
Error logging capability:        (0x01) Error logging supported.
                    General Purpose Logging supported.
Short self-test routine 
recommended polling time:    (   2) minutes.
Extended self-test routine
recommended polling time:    ( 136) minutes.
Conveyance self-test routine
recommended polling time:    (   5) minutes.
SCT capabilities:          (0x303f) SCT Status supported.
                    SCT Error Recovery Control supported.
                    SCT Feature Control supported.
                    SCT Data Table supported.

SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x002f   200   200   051    Pre-fail  Always       -       0
  3 Spin_Up_Time            0x0027   157   146   021    Pre-fail  Always       -       5108
  4 Start_Stop_Count        0x0032   098   098   000    Old_age   Always       -       2968
  5 Reallocated_Sector_Ct   0x0033   200   200   140    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x002e   200   200   051    Old_age   Always       -       0
  9 Power_On_Hours          0x0032   079   079   000    Old_age   Always       -       15445
 10 Spin_Retry_Count        0x0032   100   100   051    Old_age   Always       -       0
 11 Calibration_Retry_Count 0x0032   100   100   051    Old_age   Always       -       0
 12 Power_Cycle_Count       0x0032   098   098   000    Old_age   Always       -       2950
192 Power-Off_Retract_Count 0x0032   200   200   000    Old_age   Always       -       426
193 Load_Cycle_Count        0x0032   200   200   000    Old_age   Always       -       2968
194 Temperature_Celsius     0x0022   111   095   000    Old_age   Always       -       36
196 Reallocated_Event_Count 0x0032   200   200   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x0032   200   160   000    Old_age   Always       -       21716
200 Multi_Zone_Error_Rate   0x0008   200   200   051    Old_age   Offline      -       0

SMART Error Log Version: 1
No Errors Logged

SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed without error       00%     15444         -

Error SMART Read Selective Self-Test Log failed: scsi error aborted command
Smartctl: SMART Selective Self Test Log Read Failed
root@SERVER:/tmp# 

In one tutorial I read that the pre-fail is a an indication of coming failure, in another tutorial I read that it is not true. Can you guys help me decode the output of smartctl?

It would be also nice to share suggestions what should I do if I want to ensure data integrity (about 50GB of new data each week, up to 2TB for the whole period I'm interested in). Maybe I will go with 2x2TB Caviar Black in RAID4?