What we have done with our software is at one level similar to the 2nd gen SSD controllers, but we have a lot more resources available to us on the host. Then again, if you throw white noise writes at one of these drives over the whole surface of the drive, they still degrade a lot. They are still not 1:1, but having a couple hundred or a couple thousand IOPS for small random writes matters a lot. Thus intel, Samsung, and Indilinx controllers get better ratios. Testing with random writes verified the predicted write amplification factors based on erase block sizes.Ģnd gen SSDs have controllers that don't map the flash blocks the same way. Some of these SSDs have SMART registers that show counts for erase cycles. ![]() We have tested 1st gen SSDs with simple FTLs (Flash Translation Layers) such as jMicro controllers and MTron drives. If the average file size is smaller, then the write amplification gets bigger.Īnd remember that this slowdown is not just performance but also wear. If the average file size is larger, then the differential is smaller. In the end, with a completely unfragmented FAT32 file system, new file writes of 150K items tend to run at about 1/6th the speed of the drive if it were being updated linearly. Most run 250:1 for 4K random updates, although some cheat and can take multiple updates that are interleaved and coalesce them. Most USB sticks are not as bad as the Sandisk, but they are still terrible. You can also look at it as wearing the drive out 1000 times as fast. ![]() This literally means that the 4K update has 1/1000th the available bandwidth. For example, the SanDisk cruzer (plus a lot of CF cards) tend to update 4MB when doing a 4K write for an amplification of 1024:1. With "simple" controllers, this can result in a very high level of amplification. ![]() ![]() When you write a small block, the drive's controller has to merge the small write with existing data to update a full erase block. This leads to a characteristic called "write amplification". With USB sticks, this can easily be 1MB to 4MB in size depending on how the Flash chips are striped internally. The underlying issue with Flash is that you have a very large "erase block size".
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |