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In V16, specifically. The real question is, does a DBFileFragments value of 9,000 put the lie to a vendor's claim that "files on the EMC fiber attached SAN SSD setup we installed for you should not be defragmented"? Note that the vendor says the db file "should not be defragmented", which is different from "doesn't get fragmented"... why more salespeople don't become politicians is beyond me, they seem perfectly adept at answering questions that weren't asked :) Note also that this is related to (but different from) the long discussion here: What is the Sybase Central 16 "Fragmentation" tab showing? |
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On Windows, the DBFileFragments value comes from the OS via NtFsControlFile calls with FSCTL_GET_RETRIEVAL_POINTERS ( https://msdn.microsoft.com/en-us/library/windows/desktop/aa364572(v=vs.85).aspx ). I cannot say for sure but likely EMC claims that you don't need to defragment files because they may have sufficient caching for most cases. In particular, writes probably go immediately to RAM and they may use a battery back-up to ensure that it eventually all gets written. Having a RAID may also alleviate some of the need to defragment. It's also possible that they do some sector remapping under the covers so that fragments are relocated without Windows knowing. EMC is the only one who could give you an authoritative answer for why they claim that defragmentation is not needed. |
