25 Mar Not So TRIM SSD Drive
Previously I wrote about my Linux SSD Experience. I have been using the system for a while and have become quite accustom to SSD speeds. A 64 GByte SSD can be had for just over $100 and is well worth the investment. A typical Linux distribution takes up about 10-15 GBytes, so there is plenty of room for user files. On my system, I actually have 500 GBytes of (soft) RAID 1 just for user files the rest runs off of the SSD.
I should mention that I am running ext4 (Using Scientific Linux 6.0) so that I can use the TRIM feature of the SSD drive. TRIM is a new concept and is rather unique to SSD drives because they require an “erase cycle” before they can write to a data block. Spinning rust drives (magnetic) don’t need an erase cycle, they can write over the old data.
When asked to delete files, almost all operating systems remove the reference to the data, but do not actually “zero” out the data blocks. The deleted space is available and will be overwritten when needed. With SDD’s the situation is a little different due to the erase cycle. To improve the write times of “full” drives, TRIM allows the OS to tell the drive what data blocks are not needed. Thus, if the SSD is not busy it can “pre-release” data blocks. When it comes time to write new data, there is no need for an erase cycle. The bottom line is TRIM can help performance.
A good question to ask is, If the drive does this on its own, how do I know it is working? Indeed, this topic has been the subject of mailing lists and forums for quite a while. Fortunately, there is a very good article by Jeff Layton on the Linux TRIM issue. In addition to the long list of things you need for TRIM support under Linux, there are instructions on how to test it as well.
In my case, the program used for reading the SSD hdparm segfaults when I try to confirm TRIM support on my SSD. I’ll look into this in the future, but right now, TRIM support under Linux seems a little to brittle. It will improve and should not keep you from trying one of the new fangled SSD drives.