Hardware

Difference between SATA I, SATA II and SATA III

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What is the difference between SATA I, SATA II and SATA III?
SATA I (revision 1.x) interface, formally known as SATA 1.5Gb/s, is the first generation SATA interface running at 1.5 Gb/s. The bandwidth throughput, which is supported by the interface, is up to 150MB/s.

SATA II (revision 2.x) interface, formally known as SATA 3Gb/s, is a second generation SATA interface running at 3.0 Gb/s. The bandwidth throughput, which is supported by the interface, is up to 300MB/s.

SATA III (revision 3.x) interface, formally known as SATA 6Gb/s, is a third generation SATA interface running at 6.0Gb/s. The bandwidth throughput, which is supported by the interface, is up to 600MB/s. This interface is backwards compatible with SATA 3 Gb/s interface.

SATA II specifications provide backward compatibility to function on SATA I ports. SATA III specifications provide backward compatibility to function on SATA I and SATA II ports. However, the maximum speed of the drive will be slower due to the lower speed limitations of the port.

Example: SanDisk Extreme SSD, which supports SATA 6Gb/s interface and when connected to SATA 6Gb/s port, can reach up to 550/520MB/s sequential read and sequential write speed rates respectively. However, when the drive is connected to SATA 3 Gb/s port, it can reach up to 285/275MB/s sequential read and sequential write speed rates respectively.

Smartctl on Linux

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SMART (Self-Monitoring, Analysis, and Reporting Technology) allows you to see the status or overall health of a hard drive. This information is instumental in providing warning signs of problems with a hard drive.

All Linux distributions provide the smartmontools package, which contain the smartctl program used to display SMART information from attached drives. This package also provides the smartd daemon which periodically polls the drives to obtain SMART information.

Using smartd is essential as it can let you know immediately when a SMART attribute fails.

With the -i option, you can view the type of drive, its serial number, and so forth. In a system with a lot of drives, having this information recorded can assist in knowing which drive device (i.e., /dev/sda) corresponds with which physical drive.

Install:

# yum install smartmontools

Now start the service of Smartctl. 


#service smartd start 
# chkconfig smartd on

To enable Smart Capability for the disk run below command. 

#smartctl -s on /dev/sdb

To disable Smart Capability for the disk run below command. 


#smartctl -s off  /dev/sdb

To display details Smart info for the disk run below command. 


#smartctl -a /dev/sdb              // For IDE drive
#smartctl -a -d ata /dev/sdb       // For SATA drive

To begin, see what the drive details are:


[root@austin ~]# fdisk -l

Disk /dev/sda: 250.0 GB, 250000000000 bytes
255 heads, 63 sectors/track, 30394 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          62      497983+  83  Linux
/dev/sda2              64         584     4184932+  82  Linux swap / Solaris
/dev/sda3             585       30390   239416695   82  Linux swap / Solaris

Now we know the single drive is sda. Also, you can usually identify which hard disks are on your system by
looking in /proc/ide and in /proc/scsi.

# smartctl -i /dev/sda

root@austin ~]# smartctl -i /dev/sda
smartctl 5.43 2012-06-30 r3573 [x86_64-linux-2.6.32-504.el6.x86_64] (local build)
Copyright (C) 2002-12 by Bruce Allen, http://smartmontools.sourceforge.net

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital RE3 Serial ATA
Device Model:     WDC WD2502ABYS-18B7A0
Serial Number:    WD-WCAT19910234
LU WWN Device Id: 5 0014ee 157014252
Firmware Version: 02.03B04
User Capacity:    250,000,000,000 bytes [250 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:    Thu Nov 27 16:10:20 2014 MST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

[root@austin ~]# smartctl -i /dev/sda
smartctl 5.43 2012-06-30 r3573 [x86_64-linux-2.6.32-504.el6.x86_64] (local build)
Copyright (C) 2002-12 by Bruce Allen, http://smartmontools.sourceforge.net

=== START OF INFORMATION SECTION ===
Model Family:     Western Digital RE3 Serial ATA
Device Model:     WDC WD2502ABYS-18B7A0
Serial Number:    WD-WCAT19910234
LU WWN Device Id: 5 0014ee 157014252
Firmware Version: 02.03B04
User Capacity:    250,000,000,000 bytes [250 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:    Thu Nov 27 16:14:54 2014 MST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

Now, edit /etc/smartd.conf and add entries for your drives:


/dev/sda -d ata -H -m root
/dev/sdb -d ata -H -m root

Turn the service on:


# chkconfig smartd on
# service smartd start

The smartctl program also allows for you to view and test SMART attributes of a drive. You can quickly check the overall health of a drive by using:

# smartctl -H /dev/sda

smartctl can be used to initiate long and short tests for the drive. These should be run periodically to do quick, or full, self-tests of the drive:


# smartctl --test=short /dev/sda
# smartctl --test=long /dev/sda
# smartctl -a /dev/sda

More info : https://wiki.archlinux.org/index.php/S.M.A.R.T.

PHP Sessions causing Error

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Currently your messages log is filling up with errors and the system is unstable. Check the message log:

$ server# tail -f /var/log/messages
Jul 28 08:57:30 mail kernel: EXT4-fs warning (device sda3): ext4_dx_add_entry: Directory index full!

Check the sessions directory

 $ server# php -i | grep session.save_path
session.save_path => /var/lib/php/session => /var/lib/php/session


$ server# du -shcx /var/lib/php/session
1000.0M    /var/lib/php/session
1000.0M    total

A cron job similar to the following ran every day, or periodically, should prevent those files from accumulating.


# find /var/lib/php/session -type d -mtime -15 -delete

Manually

# find /var/lib/php/session -depth -mindepth 1 -maxdepth 1 -type f -cmin +120 -delete;

Check disk IO

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To check disk IO:

dd bs=1M count=512 if=/dev/zero of=test conv=fdatasync
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 5.57475 s, 96.3 MB/s

Hard Drive Tools

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With respect to hard drives, the acronym “SMART” stands for Self-Monitoring, Analysis and Reporting Technology. This was built into many ATA-3 and later ATA, IDE and SCSI-3 hard drives. Basically anything after about 2005 should have it.

Ubuntu/Debian:

sudo apt-get install smartmontools

CentOS/Fedora/RH:

sudo yum install smartmontools

Gentoo:

sudo emerge sys-apps/smartmontools

Wiki: http://sourceforge.net/apps/trac/smartmontools/wiki

smartctl

The program smartctl is used to interface with the SMART features on the drive firmware. Here are a couple of easy things to get started with (however some versions do not have the –scan option):


$ smartctl --scan -d ata
/dev/hda -d ata # /dev/hda, ATA device
/dev/hdc -d ata # /dev/hdc, ATA device
$ sudo smartctl --info /dev/hdc
smartctl 5.42 2011-10-20 r3458 [i686-linux-2.6.33.1-xedvia] (local
build)
Copyright (C) 2002-11 by Bruce Allen,
http://smartmontools.sourceforge.net

=== START OF INFORMATION SECTION ===
Model Family:     Seagate Barracuda 7200.7 and 7200.7 Plus
Device Model:     ST3160023A
Serial Number:    5JS9MDKW
Firmware Version: 8.01
User Capacity:    160,041,885,696 bytes [160 GB]
Sector Size:      512 bytes logical/physical
Device is:        In smartctl database [for details use: -P show]
ATA Version is:   6
ATA Standard is:  ATA/ATAPI-6 T13 1410D revision 2
Local Time is:    Thu Feb  7 09:27:18 2013 PST
SMART support is: Available - device has SMART capability.
SMART support is: Disabled

Note that the “SMART support” is listed as available but disabled. To enable full diagnostic checking turn it on with something like this:


$ sudo smartctl --smart=on --offlineauto=on --saveauto=on /dev/hdc
=== START OF ENABLE/DISABLE COMMANDS SECTION ===
SMART Enabled.
SMART Attribute Autosave Enabled.
SMART Automatic Offline Testing Enabled every four hours.

In theory this should only need to be done once and the drive should remember this (because of the saveauto directive). The offlineauto will cause automatic testing every 4 hours. In theory it will wait “nicely” if the drive is already busy so performance should not be seriously impacted.
Testing

Here’s a way to run a “short” off-line test. This tests electrical and mechanical performance of the drive and does read testing.


$ sudo smartctl --test=short /dev/hda
=== START OF OFFLINE IMMEDIATE AND SELF-TEST SECTION ===
Sending command: "Execute SMART Short self-test routine immediately in off-line mode".
Drive command "Execute SMART Short self-test routine immediately in off-line mode" successful.
Testing has begun.
Please wait 1 minutes for test to complete.
Test will complete after Thu Feb  7 10:13:19 2013
Use smartctl -X to abort test.

$ sudo smartctl --log=selftest /dev/hda
=== START OF READ SMART DATA SECTION ===
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%     43398        -

$ sudo smartctl --log=selftest /dev/hdc
=== START OF READ SMART DATA SECTION ===
SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining  LifeTime(hours)  LBA_of_first_error
# 1  Short offline       Completed: read failure       90%     37994         7234643

The first command starts the test off and it tells you to come back in 1 or 2 minutes. The second command shows how to query the log file to see if anything bad came up. In this case hda was fine (“Completed without error”) but hdc had a very important “read error”. Replace that drive ASAP!