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Corsair Performance Series Solid State RAID Report

By: Chris Ramseyer | RAID in Storage | Posted: Jul 27, 2009 3:19 am

Samsung's Self-Healing, Defragment for the Modern Age


I have talked a lot about the differences between Single-Level Cell (SLC) and Multi-Level Cell (MLC) technology extensively in other reviews, so I will only give a brief recap here. Up until a few months ago SLC drives were kicking the expletive out of MLC drives in write speeds. One of the reasons for this is that MLC drives need to perform an extra operation before writing a block of data. To those of us without a masters degree in whatever type of engineering this would fall under, we call it erase.


Let's say you had a file on your desktop that you no longer needed. You right click on it, delete it and then delete it from your recycle bin. In Windows it is kind of like moving from one house to another, the name on the mailbox has been removed but the house still stands. For MLC drives, before a new house can be built the old house has to be bulldozed and this takes time.


The early J-Micron controlled drives had a real problem with this since they only had 16KB of cache to buffer incoming data. Luckily the latest round of Samsung controllers has 128MB of cache, making the stuttering problem a thing of the pppppaassssstttt. Even though modern drives have a sufficient amount of cache, the underlying issue remains, the block has to be erased.


In our testing we found that no matter the controller, be it Intel, Indilinx or Samsung, if a block has been occupied with data the next write operation can only achieve between 70 and 80 MB/s. That is a long ways from the highest performing drives claimed write speeds of 200+ MB/s.


Many companies are trying to stay silent about the issue and are anxiously waiting for Windows 7 to be released since it is claimed to have a TRIM feature built into the operating system. Samsung is a big company with deep R&D resources and they decided that they didn't need to wait for Microsoft to release Windows 7 to fix an issue in their house.


Samsung's Self-Healing feature is not found in a DOS application, Windows executable or any other user activated program. Self-Healing is built into the second generation Samsung controller and automatically trims the fat from the SSD bone. The only real down side that I was able to find with Self-Healing is that it happens when the system is idle. Then again, when I am working or surfing on YouTube I don't really want my drive searching out useless data. Windows Defender seems to be doing that all the time already.


Since Self-Healing is handled by the drive itself, the technology is active, even in RAID arrays. This is a feature that should work out well for power users who are taking SSDs and putting them in blazing fast RAID arrays, like we are doing here today.


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