Solid-State Drive Best Practices On Mac OS

DENVER - May 31, 2013 - PRLog -- SSDs (solid-state drives) are being more widely used in consumer computers as their pricing falls and capacities increase.  Like most technology, prices of the solid state drives went down after a while; thank goodness! The Tech Report made a graph that shows the price per gigabyte (GB) of the most currently popular SSDs. Some of the SSDs listed at the top of this graph show their prices are below $1 per GB. That’s within the price range of platter-based drives – this means SSDs have started to become viable substitutes to traditional hard drives for consumer computer products.

By The Tech Report

The Tech Report research in June 2012 found that prices for solid-state drives have dropped 48% since the previous year.

The solid-state drives were made popular by Apple’s MacBook Air and were touted for their durability and resistance to physical damage due to the non-moving parts.   As a result SSDs are becoming more popular for laptops and portable computers.

The benefits of these drives include:

Less power usage
Less heat generation
Reduced potential for mechanical damage
Faster performance when compared with mechanical drives

With these perks it’s no surprise that they have sparked an increase in SSDs in all computers from laptops to consumer and pro desktop systems. But you can’t always have your cake and eat it too.  There are a few issues that may arise when using a SSD in your computer.

Although the performance is a major advantage to SSDs, there are a couple things to watch out for that can possibly result in degraded SSD drive performance on Macs.

The problem of degraded SSD performance on Macs is due to the technology behind solid state drives in that over time and use, the speed of the drive will start to slow down. The main reason for this is the SSD needs to be in an “empty” state before it can reliably accept data.

When it comes to a solid-state drive the system does not remove the actual data every time data is deleted from a drive, instead it just frees additional blocks to be overwritten. SSDs do this by modifying the drive’s index and directory files.

SSDs use NAND memory, which is organized into PAGES, which are then organized into BLOCKS. Different operations are executed on different levels of organization on the NAND memory.  For example, a write operation is done on a page, and a delete operation is done on a block, which becomes a problem when the drive starts running out of pages.  When this happens, the drive controller will need to recover some of the previously deleted pages.

In mechanical drives this is not a problem because the drive can easily write over used blocks, while modifying them to contain the new data in one fell swoop. In SSD drives, however, the blocks containing unused data needs to be properly erased and set to a “ready” state before accepting new data.

The following steps are required for the drive controller to recover the files:

Copy any data on the pages in the block that are not marked for deletion into its cache
Once in the cache the controller will need to update the data marked for deletion
Free up the “real” block
Write the cache copy into the “real” block

This process will eventually lead to a situation known as “write amplification”, where unnecessary page writes occur, shortening the life span of the SSD.  There are a limited number of erase/write cycles for each SSD, and write amplification will accelerate the solid-state drive towards that limit. Write amplification results in the actual amount of physical information written being a multiple of the logical amount that was supposed to be written. This multiplying effect increases the number of writes required over the life of the SSD shortening the time it can reliably operate.

When you purchase a new SSD, they already have the storage blocks in a ready state, resulting in the drives being very fast. But, as the drive’s blocks get progressively filled through use, the number of blocks that are left in the “ready” state will drop until eventually all writing processes by the system will have to wait for the drive to first reset the blocks being used. The decrease in performance may not necessarily make your system feel like it’s crawling, or even as slow as the speed of mechanical hard drives, but it may be noticeably slower than the initial performance rate.

To deal with this problem solid-state drive manufacturers and various OS developers are including procedures that will slowly reset unused blocks on the drives in the background when the drives are not being accessed. These routines include the “TRIM” and “Secure Erase” ATA commands that, if supported in the drive’s firmware, can be triggered by a software protocol to perform the block resetting procedure on the drive.

The support for these block resetting routines has only been implemented for the latest MacBook Pro systems, and only for SSD drives that are shipped already installed in the systems. This means that if you purchase a third-party SSD drive that supports TRIM, OS X will not use this feature. Therefore, the best method for cleaning up and reconditioning SSD drives in OS X has been to do various erase routines that will reset the SSD blocks.  Here are a few ways to do this:

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