A Primer for Laptop SSD Buyers (draft)

This blog entry attempts to assist the mobile user as he/she begins to search for an SSD replacement for his/her existing rotational drive.

Components:

Every drive has it’s own Controller, MLC NAND, and firmware features.  Every manufacturer puts each drive line together using using these building blocks.  Each aspect of the Controller, the NAND, and the Firmware have profound effects on a drive’s performance, longevity, and interoperability with the operating system supporting it.

The controllers are manufactured by: Sandforce, Samsung, Indilinx (Barefoot & Amigos), and Jmicron.  Each controller manufacturer may have several models of controllers to pick from.  The most popular consumer controllers at the moment are: Indilinx IDX110M00-FC “Barefoot”, Intel PC29AS21AA0, JMicron JMF612, Toshiba T6UG1XBG, Samsung S3C29RBB01-YK40, Marvell 88SS8014-BHP2, SandForce SF-1200/1500, and now the Marvell 88SS9174-BJP2 SATA-III SSD controller.  Samsung & Indilinx seem to have the best reputation for “studder-free” performance.  Samsung’s controller is in it’s second version.  Indilinx has been around the longest and is referred to as “stutter free, has integrated cache, and provides “smooth operation”.  Sandforce has introduced “DuraClass Technology” in its controllers (SF-1500, and the lower cost, lower performance SF-1200)  and firmware set to offer an entirely new way to commit data into the NAND Flash Array (more on this below).  It is so revolutionary that it virtually eliminates the need for TRIM.

The Multi Layer Cell NAND comes from: Jmicron, Samsung, & Intel.  Each NAND manufacturer, of course, has various MLC sets of varying speeds and densities.

The firmware can contain leveling code in addition to support for TRIM (an a standardized approach to “telling” the OS which cells are available for writing.  If the OS supports TRIM, then the drive does not need to manage cell usage, the OS will take over.)  Other features include garbage collection (the process of moving data from “used” cells into other cells to make incoming writes more efficient), power management, TRIM management, data protection algorithms for reducing data loss in light of power failure, data management to reduce maximum write latency, “full drive” data management features to increase performance as the drive reaches capacity.

Examples of controllers and which drives use them:

Samsung S3C29RBB01-YK40 (second generation Samsung controller):
Samsung PB22-J
Corsair Performance Series (seems to actually BE the Samsung PB22-J)

SandForce SF-1200 or SF-1500:
A-Data S599 Series
Corsair Force Series
Mushkin Callisto Series
OCZ Vertex LE Series
OCZ Vertex 2 Series
OCZ Agility Series
RunCore Pro-V Series
Super Talent TeraDrive Series
Unigen
AMP SATAsphere Series
IBM
Viking

Indilinx Barefoot:
Nearly every “mainstream” second-generation drive uses the Barefoot
OCZ Vertex Series
Crucial M225
Corsair Nova (V) and Reactor

Here is a matrix of the OCZ drives, the speeds, and controllers they use: http://www.ocztechnology.com/res/manuals/OCZ_%20SSDs_quick_compare_5.pdf
 

What to Look for in a drive:

Drives should be of the appropriate size for only those things that you want to run quickly.  For example, you may not want to store your 90GB music files on an SSD, but you will want to store your Operating System and paging file on an SSD.  You may want to store your multi-megabyte jpeg and raw photo files on SSD depending on what you are doing with them, i.e. editing, tagging, etc.

Drives should have an algorithm to avoid pre-mature aging.  Some drives have Background garbage collection routines.  While BGC does increase the overall write performance of your drive over time, it also shortens its life by over-using the cells as it relocates data.  TRIM is an OS-enabled partnership with the drive that allows the OS to understand which cells are “best” to write to at any moment.  TRIM promises to extend the life of drives by avoiding cell over-use and premature cell aging.  TRIM is loaded with faults however and is really intended for workstations and laptops.  TRIM does nothing to solve the long-term performance and durability of drives installed inservers and under RAID controllers.  To solve the issues of long-term performance stability and drive durability, other controller manufacturers have approached the issue from a completely new direction — see Write Amplification below.

Speed is certainly a concern for every SSD.  Several controllers directly address performance enhancements in several ways: 1) Throughput in IOs/s, 2) Bandwidth in MB/s, and then the notion of sustained performance.  Every controller manufacturer has new controllers (since mid-2009) that bring read and write performance into the 200MB/s range.  A small number of controller and Single Layer Cell combinations can bring performance over 300MB/s.

Firmware support is crucial (no pun intended).  Firmware updates allow the manufacturers to add features like TRIM, power management, and ECC recovery algorithms.  Almost every drive manufacturer has allowed for firmware updates to their drives.  The downside is that nearly every vendor currently dictates a complete re-initialization of the drive — total loss of every bit of data on the drive — a complete reload is necessary after the firmware is installed.  Manufacturers such as Crucial are working to avoid this inconvenience in the future firmware releases.

Price is always a concern.  SandForce, for example has released a new version of their amazing SF-1500 controller and firmware set in an attempt to compete with lower cost controllers from Indilinx (for example).  the new SF-1200 controller offers reduced performance compared to the SF-1500, but still offers SandForce’s DuraClass write leveling technology at a substantially lower cost.

A look at Specific Drives:

Crucial, Corsair, Intel, and OCZ all have their latest firmware sets, some drives were able to receive new firmware, other previous generation drives could not implement all the new feature sets.

Below is an example of firmware updates from Crucial.  The Crucial M225 and RealSSD C300 got firmware updates this year (January and May respectively).  Both drives have added support for TRIM.  You might notice that the M225 has added/modified their “wear leveling algorithm”.  These algorithms go above and beyond what TRIM provides.

RealSSD C300 (Marvel SATA-III controller)

Release Date: 5/20/2010
Change Log:
Improved Power Consumption
Improved TRIM performance
Enabled the Drive Activity Pin (Pin 11)
Improved Robustness due to unexpected power loss
Improved data management to reduce maximum write latency
Improved Performance of SSD as it fills up with data
Improved Data Integrity

M225 (Indilinx Barefoot controller)
Release Date: 1/21/2010
Change Log:
Fixed issue that sometimes causes firmware download problem
Fixed issue that could cause 256GB to be corrupted
Eliminated performance degradation over time with Wiper with 1819 FW
Fixed issue where the power cycle count was incorrectly being reported with 1819 FW
Fixed issue where some SATA 1 hosts weren’t correctly identifying the hardware
Fixed issue found in simulation (not in the field) where the free block count was incorrectly being reported
Fixed issue with remaining life not being properly displayed on SMART information
Added support for additional NAND manufactures and capacities
Made further improvements to wear leveling algorithm

Corsair Performance Series (P256)
Has a Samsung controller and Samsung-provided firmware

The “Force” series of drives from Corsair are based on the SandForce SF-1200; they were introduced in May of 2010 so this technology is really new and revolutionary. http://www.sandforce.com/index.php?id=19&parentId=2
OCZ also uses the SandForce controllers (the Vertex Limited Edition line uses the higher-end SF-1500 controller, while the Vertex 2, and Agility 2 lines use the less expensive SF-1200 controller).

Corsair has a great blog entry describing “write amplification”: http://blog.corsair.com/?p=3044

The SandForce controller mentioned above brings DuraClass Technology to market… Here’s an excerpt from Kevin Conley’s blog at Corsair:SandForce demonstrated that through its innovative DuraClass technology, Write Amplification factors below 1 could actually be achieved. Not only that but also without the use of a large (and expensive) external Data Cache. As noted in some other blogs, this data intelligence utilitizes data-dependent compression techniques coupled with other “secret sauce” algorithms to reduce the amount of data to write in the first place, in some cases quite significantly. The SandForce SSD processor then manages the programming of data using very efficient Page Management algorithms that prevent the need for Garbage Collection down the road. The net result of this is a Write Amplification much lower than other SSD controllers achieve, and thus the screaming fast write performance demonstrated by the Corsair Force Series solid-state drives. This is an even more amazing feat when considering these SSDs use MLC memory but compete with enterprise-class solutions utilizing much faster SLC memory.

Drives I would buy (based on price, speed, and durability/longevity:
OCZ Vertex 2 (SF-1500) – up to 50,000 4k IOPS
OCZ Vertex LE (SF-1500 LE)
OCZ Agility 2 (SF-1200) – up to 10,000 4k IOPS
Mushkin Callisto (SF-1200)
Corsair Force (SF-1200)



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