How to on the smart support?

smart -h showed me what to do

smartctl --smart=on --offlineauto=on --saveauto=on /dev/hda (Enables SMART on first disk)

I just changed the same to

sudo smartctl --smart=on --offlineauto=on --saveauto=on /dev/sdb

which gave me

shirish@Mugglewille:~$ sudo smartctl --smart=on --offlineauto=on --saveauto=on /dev/sdb
smartctl version 5.37 [i686-pc-linux-gnu] Copyright (C) 2002-6 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF ENABLE/DISABLE COMMANDS SECTION ===
SMART Enabled.
SMART Attribute Autosave Enabled.
SMART Automatic Offline Testing Enabled every four hours.

Now my query is what is this SMART Automatic Offline Testing which I have enabled every 4 hours?

Some more info.

shirish@Mugglewille:~$ sudo smartctl -d ata -a /dev/sdb
smartctl version 5.37 [i686-pc-linux-gnu] Copyright (C) 2002-6 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Device Model: SAMSUNG SP0802N
Serial Number: S00JJ10X390473
Firmware Version: TK100-24
User Capacity: 80,060,424,192 bytes
Device is: In smartctl database [for details use: -P show]
ATA Version is: 7
ATA Standard is: ATA/ATAPI-7 T13 1532D revision 0
Local Time is: Sun Jun 1 19:50:37 2008 IST
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: (0x80) Offline data collection activity
     was never started.
     Auto Offline Data Collection: Enabled.
Self-test execution status: ( 0) The previous self-test routine completed
     without error or no self-test has ever
     been run.
Total time to complete Offline
data collection: (2880) seconds.
Offline data collection
capabilities: (0x1b) SMART execute Offline immediate.
     Auto Offline data collection on/off support.
     Suspend Offline collection upon new
     command.
     Offline surface scan supported.
     Self-test supported.
     No Conveyance Self-test supported.
     No 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.
     No General Purpose Logging support.
Short self-test routine
recommended polling time: ( 1) minutes.
Extended self-test routine
recommended polling time: ( 48) minutes.

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 0x000b 100 100 051 Pre-fail Always - 0
  3 Spin_Up_Time 0x0007 078 041 000 Pre-fail Always - 4224
  4 Start_Stop_Count 0x0032 091 091 000 Old_age Always - 9510
  5 Reallocated_Sector_Ct 0x0033 253 253 010 Pre-fail Always - 0
  7 Seek_Error_Rate 0x000b 253 253 051 Pre-fail Always - 0
  8 Seek_Time_Performance 0x0024 089 087 000 Old_age Offline - 10302
  9 Power_On_Half_Minutes 0x0032 098 098 000 Old_age Always - 14524h+43m
 10 Spin_Retry_Count 0x0013 253 253 049 Pre-fail Always - 0
 12 Power_Cycle_Count 0x0032 095 095 000 Old_age Always - 5079
194 Temperature_Celsius 0x0022 103 082 000 Old_age Always - 45
195 Hardware_ECC_Recovered 0x000a 100 100 000 Old_age Always - 145292381
196 Reallocated_Event_Count 0x0012 253 253 000 Old_age Always - 0
197 Current_Pending_Sector 0x0033 253 253 010 Pre-fail Always - 0
198 Offline_Uncorrectable 0x0031 253 253 010 Pre-fail Offline - 0
199 UDMA_CRC_Error_Count 0x000b 100 100 051 Pre-fail Always - 0
200 Multi_Zone_Error_Rate 0x000b 100 100 051 Pre-fail Always - 0
201 Soft_Read_Error_Rate 0x000b 100 100 051 Pre-fail Always - 0

SMART Error Log Version: 1
ATA Error Count: 5686 (device log contains only the most recent five errors)
 CR = Command Register [HEX]
 FR = Features Register [HEX]
 SC = Sector Count Register [HEX]
 SN = Sector Number Register [HEX]
 CL = Cylinder Low Register [HEX]
 CH = Cylinder High Register [HEX]
 DH = Device/Head Register [HEX]
 DC = Device Command Register [HEX]
 ER = Error register [HEX]
 ST = Status register [HEX]
Powered_Up_Time is measured from power on, and printed as
DDd+hh:mm:SS.sss where DD=days, hh=hours, mm=minutes,
SS=sec, and sss=millisec. It "wraps" after 49.710 days.

Error 5686 occurred at disk power-on lifetime: 14524 hours (605 days + 4 hours)
  When the command that caused the error occurred, the device was active or idle.

  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  04 51 01 01 4f c2 10 Error: ABRT

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name
  -- -- -- -- -- -- -- -- ---------------- --------------------
  b0 d1 01 01 4f c2 10 00 02:44:43.813 SMART READ ATTRIBUTE THRESHOLDS [OBS-4]

Error 5685 occurred at disk power-on lifetime: 14524 hours (605 days + 4 hours)
  When the command that caused the error occurred, the device was active or idle.

  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  04 51 01 00 4f c2 10 Error: ABRT

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name
  -- -- -- -- -- -- -- -- ---------------- --------------------
  b0 d0 01 00 4f c2 10 00 02:44:43.813 SMART READ DATA

Error 5684 occurred at disk power-on lifetime: 14524 hours (605 days + 4 hours)
  When the command that caused the error occurred, the device was active or idle.

  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  04 51 f1 00 4f c2 10 Error: ABRT

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name
  -- -- -- -- -- -- -- -- ---------------- --------------------
  b0 d2 f1 00 4f c2 10 00 02:44:43.750 SMART ENABLE/DISABLE ATTRIBUTE AUTOSAVE

Error 5683 occurred at disk power-on lifetime: 14524 hours (605 days + 4 hours)
  When the command that caused the error occurred, the device was active or idle.

  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  04 51 00 00 4f c2 10 Error: ABRT

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name
  -- -- -- -- -- -- -- -- ---------------- --------------------
  b0 da 00 00 4f c2 10 00 02:44:43.750 SMART RETURN STATUS

Error 5682 occurred at disk power-on lifetime: 14524 hours (605 days + 4 hours)
  When the command that caused the error occurred, the device was active or idle.

  After command completion occurred, registers were:
  ER ST SC SN CL CH DH
  -- -- -- -- -- -- --
  04 51 00 00 4f c2 10 Error: ABRT

  Commands leading to the command that caused the error were:
  CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name
  -- -- -- -- -- -- -- -- ---------------- --------------------
  b0 da 00 00 4f c2 10 00 02:44:43.750 SMART RETURN STATUS
  ec 00 01 00 00 00 10 00 02:44:43.750 IDENTIFY DEVICE
  ec 00 01 00 00 00 10 00 02:44:43.688 IDENTIFY DEVICE
  ca 00 08 c7 bc 01 f0 00 02:44:43.688 WRITE DMA
  ca 00 10 b7 bc 01 f0 00 02:44:43.688 WRITE DMA

SMART Self-test log structure revision number 1
No self-tests have been logged. [To run self-tests, use: smartctl -t]

Device does not support Selective Self Tests/Logging

The last line is important, what does it mean that it doesn't support self tests/logging can anybody explain?

Hello

This link has a nice description on smart

http://www.linuxjournal.com/article/6983

Regards

Bhavani Shankar.