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     SandForce & Trim: listen up!
      Posted on 26/05/2010 at 10:31 by Marc
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    Since our article on TRIM and IOMeter, we have been running numerous SSDs through their paces so as to be able to best advise you. For the last month, we have among others had an SSD based on the SF-1200, the OCZ Vertex 2, but have been trying to resolve a to-say-the-least, strange problem, especially as it had never previously come up in the already numerous tests, particularly on UK and American sites, published on this controller.

    In effect, while the TRIM command had the expected impact on this SSD when we were using the Intel RST drivers, this wasn’t the case with the standard Microsoft Windows 7 drivers. This is rather problematic as with official Marvell and AMD drivers not supporting TRIM, the Microsoft drivers are the only TRIM compatible solution for non-Intel chipsets.

    We have been in contact with OCZ who have been working with SandForce over the last fortnight to identify the problem. They have now done so successfully and here is the explanation that SandForce has given us.

    First of all, you need an understanding of how the TRIM command works. With the command, the driver sends a group of addresses to the SSD which no longer correspond to data. Each group or “sector” contains 64 entries and for each of these entries is specified the starting LBA and the number of sequential addresses behind it that are also affected, up to 65536. Via the Identify Device data word 105, SandForce tells the AHCI driver that it doesn’t accept more than a group of 64 entries at a time, a parameter that is respected by the Intel RST driver.

    However the Microsoft TRIM driver doesn’t respect this and continues to send 4 to 8 sectors at a time, which doesn’t comply with the latest ATA standard according to SandForce and goes beyond the specifications of the SSD exposed to the driver, which means that these commands aren’t accounted for by the SSD. This is why on SandForce SSDs TRIM only works with the RST drivers!

    SandForce has told us that it will introduce a workaround that should address most of the issues associated with the Microsoft Driver implementation, but not all, as for instance it wont trim the entire SSD on a quick format. Ultimately, SandForce says, the best result would be for Microsoft to update their driver to comply with the latest ATA standard. SandForce says that they are in dicussions with Microsoft on this subject.

    In the meanwhile, in view of the importance of the TRIM command, we can only advise you not to buy an SSD based on a SandForce controller for platforms other than Intel.


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