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SSD Defrag ?
On 12/4/2018 3:58 PM, Paul wrote:
David E. Ross wrote: On 12/4/2018 3:08 PM, Paul wrote: wrote: Appreciate all the info, but not sure I have a clear answer. Is there no issue at all, accessing a very fragmented file, compared to accessing an unfragmented file, on an SSD ? Here are some test results. https://i.postimg.cc/ry7VnwF7/fragmentation.gif 26GB test file Checksum used as a read test of the file. Fragmented file has around 396,000 fragments. Unfragmented file is contiguous. On a RAMDISK (close to zero seek) 970MB/sec fragmented read 993MB/sec unfragmented read On an SSD where a 20usec seek time 229MB/sec fragmented read is present, so 396000 of the 20usec 383MB/sec unfragmented read seeks are required. That's to give some idea how much effect an extremely fragmented file would have on an SSD. Paul A fragmented drive takes longer to read than an unfragments (defragmented) drive??? Yes, the extra time to seek from one chunk of the file to the next. XXXXXXX XXXXXXX XXX XXXXXXXXXXXX \____ Wasted time reduces 20us 20us 20us / aggregate bandwidth (SSD) On a hard drive, it's much worse. Head switches cost 1ms, seeks are more expensive. XXXXXXX XXXXXXX XXX XXXXXXXXXXXX \____ Wasted time reduces 8ms 8ms 8ms / aggregate bandwidth (HDD) On my RAMDisk (I haven't measured it), it should be around these numbers. These would be typical numbers for a "hardware" RAM drive. The OS software stack probably degrades numbers like this quite a bit. XXXXXXX XXXXXXX XXX XXXXXXXXXXXX \____ Wasted time reduces 2us 2us 2us / aggregate bandwidth (RAM Drive) HTH, Paul Your two examples illustrate fragmentation. Unfragmentation is obtained by deframenting, which yields files with their contents contiguous. -- David E. Ross http://www.rossde.com/ Once again, there has been a mass shooting. This time, it was in Thousand Oaks, California. And once again, just as he did after the recent mass shooting in Pittsburgh, President Trump sent his thoughts and prayers to the families of the victims. Thoughts and prayers will not stop the carnage. Action is needed on gun control, and more guns -- as Trump proposed for Pittsburgh and Parkland in Florida -- is not the answer. |
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