Horse Sense #99

Solid State Drives (SSDs) Are NOT

Like Standard Hard Disk Drives (HDDs)

In this issue of Horse Sense:
-Comfortable Computing
-Solid State Drives (SSDs) Are NOT Like Standard Hard Disk Drives (HDDs)
Data Recovery and SSDs


Comfortable Computing

If you want to improve your life in front of your computer, take note of how to use it most comfortably.  These articles may help:

Don't forget to use a headset for talking on your phone.

Solid State Drives (SSDs) Are NOT Like Standard Hard Disk Drives (HDDs)

You are probably already using solid state technology.  All cell phones, tablets, hand held gaming toys, electronic readers, memory sticks, and many other devices use solid state storage.  Usually this storage is lower performing and less reliable than what we think of as an SSD for a PC, notebook, or server.  SSDs are an enhanced form of solid state storage technology designed to look like traditional hard disks to operating systems and contain a lot of intelligence, reliability, and other features built into them that simple solid state storage lacks.  When solid state storage is used in this article, it means either the dumb stuff.  When SSDs are mentioned, know that the smarter storage is meant.

The dominance of HDDs is fading.  You need to know how SSDs work.  2011 SSD storage revenue was more than twice that of 2010 and is still accelerating.  Smaller form factor devices requiring large amounts of high performance storage, small form factors, low power draws, and little heat generation, like portables and Ultrabooks (Intel trademarked name for new generation notebooks with specific properties) demand SSDs.  In addition, the disruption of hard drive production has raised the price and lowered the availability of HDDs, making SSDs more attractive.  In fact, Lenovo, the second biggest PC maker in the world, recently offered to swap in a 160GB SSD into their most popular laptop models for an extra $100.  Since most laptops do not need a huge amount of storage, this is an excellent deal.

Tiered storage has become popular.  Marrying SSDs and HDDs together leverages the speed of SSDs with the low cost per unit of storage of HDDs.  Often, SSDs are used as large cache devices to hold the most often used information on the HDDs, speeding overall access times.  This situation will only last as long as HDDs maintain a significant price advantage.  Already SSDs are being made with the same amount of storage as the largest HDDs.  If the cost on them drops far enough, no one will build hybrid drives or tiered storage containing both types of drives.  I do not expect that to happen in the next couple of years, but SSD pricing per gigabyte is dropping rapidly.  About a year ago, SSDs that I looked at cost twice as much money for the same amount of storage and they were half as fast.  Meanwhile, HDDs pricing dropped for a while and then went up due to the disaster in Thailand and performance remained about the same.  HDDs are not immediately doomed, but their days are numbered.

Data Recovery and SSDs

DriveSavers did a seminar on data recovery for solid state memory.  They brought up some interesting points, but the biggest take away was that SSDs are not like standard HDDs.  For example, many of the ways a standard HDD might fail simply do not exist on an SSD.  They are inherently more reliable.

You do not have to make solid state storage like a hard drive or use a hard drive interface.  SSDs exist that look just like RAM sticks.  This allows you to make smaller and thinner drives that don't need a case around them.  You can also put the chips right on a motherboard or on a hard drive controller board, as Seagate does with their hybrid Momentus XT hard drive, or simply build an add in card and populate it with chips to make a blazingly fast SSD like OCZ does.  Because of the many different forms solid state storage can take, recovery is not as simple as it is with HDDs.

SSDs, like HDDs, can be corrupted if power is removed before the operating system can complete writing to the disk.  However, newer SSDs are now being produced that carry super capacitors on them.  If power is removed, these capacitors are engaged and can provide enough power to finish all the writes to the disk.  You cannot really do this with an HDD, so SSDs gain another reliability advantage.

Because SSDs are newer, they tend to incorporate the latest ideas on how to store information already built into them.  For example, many SSDs can encrypt/unencrypt and compress/decompress data transparently, allowing for more secure information storage and higher densities and throughputs.  There are downsides to some of these technologies as well.  For example, if you lose the encryption key to a self-encrypting HDD or SSD, the data is effectively gone forever.  Not only is it safe from the bad guys, but it is safe from you as well!  In some of the new SSDs and HDDs on the market, encryption is turned on by default in the hardware.  Your only salvation will be to save those keys and keep them backed up in a safe and secure location.

You do not write to an SSD like you do to an HDD.  When you write to a HDD, you just overwrite what is there.  When you write to an SSD, you clear the area first and then write to it.  This is why it takes more time to write to an SSD than read from it.  To avoid this write penalty, SSD drive makers often implement a function called TRIM.  The operating systems must understand TRIM.  Windows 7 does, but Windows XP does not.  That operating system must also speak to SSDs that understand TRIM.  A TRIM aware operating system issues a command to a TRIM enabled SSD that tells it to clear the area at the time the data is deleted so that you can later write to it without penalty.  Since you clear the area after the deletion, you cannot undelete the file like you can with HDDs.  With an HDD, you remove the pointer to the data, but the information is still there until you overwrite it.  With an SSD using TRIM, not only do you remove the pointer, but you remove the data as well.

Recovering deleted data becomes even more problematic when you consider that SSDs often also perform garbage collection and wear leveling as well.  Garbage collection basically does the same thing as TRIM does, but the drive does it without being asked by the operating system.  Over time, an "idle" SSD will use that time to remove deleted information to make the area available for quick writing.  In addition, a drive may also wear level by spreading write requests throughout the entire drive and even moving data from one location to another.  This is because you may only be able to write to a certain area 10,000 times.  If you were to write to that area once, then the rest of the available area would wear out faster.  To make the SSD wear more evenly, data is moved so that writes are spread equally about the disk, leveling the playing field and allowing the disk to handle more total writes.

SSDs and HDDs are alike in that they reserve space in case a part of the disk goes bad.  That reserved space is swapped in for the bad space and the bad space is locked out.  Typically, though, for both performance and reliability reasons, SSDs reserve more space just in case.

SSDs, but not solid state memory devices or HDDs, have a secure erase function built right into the drive.  With a typical hard disk, if you want to make sure all the data is gone, you have to make sure you overwrite every part of the disk.  In fact, US Department of Defense regulations require you to do this multiple times.  With an SSD, you issue one command and the SSD blanks itself by clearing all its memory cells as if preparing for a write.

Another instance where all your data could end up being gone forever is a factory reset on solid state storage.  If you factory reset your cell phone, it will rewrite its configuration and clear all the other space rendering what was there unrecoverable.

DriveSavers ended its presentation the way all good IT people do when talking about data reliability by saying "Back up your data and encryption keys."  If you do not do this, or a disaster happens, you may have to pay for their rather pricey services and they may or may not be able to get your precious data back.


©2012 Tony Stirk, Iron Horse<