Perché WriteFile chiama ReadFile e come posso evitarlo?

Question

Se si sovrascrivono in sequenza (ad esempio 8192 byte allineati e blocchi di dimensioni) nelle parti esistenti di un file (a volte/sempre?) WriteFile causa la lettura di file da disco, che distrugge completamente le prestazioni. Non capisco perché questo accada e come evitarlo.

Utilizzando Process Monitor ho ottenere le seguenti informazioni:

Event.Class: File System 
Event.Operator: ReadFile 
Event.Offset: 1 875 288 653 824 
Event.Length: 4 096 
Event.I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O 
Event.Priority: Normal 

0 FLTMGR.SYS FltDecodeParameters + 0x1ab1 0xfffff8016e7f4621 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
1 FLTMGR.SYS FltDecodeParameters + 0x166c 0xfffff8016e7f41dc C:\WINDOWS\System32\drivers\FLTMGR.SYS 
2 FLTMGR.SYS FltDecodeParameters + 0x1093 0xfffff8016e7f3c03 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
3 FLTMGR.SYS FltDecodeParameters + 0xe8e 0xfffff8016e7f39fe C:\WINDOWS\System32\drivers\FLTMGR.SYS 
4 ntoskrnl.exe IoPageRead + 0x258 0xfffff8015b8ba598 C:\WINDOWS\system32\ntoskrnl.exe 
5 ntoskrnl.exe IoPageRead + 0x4d4 0xfffff8015b8ba814 C:\WINDOWS\system32\ntoskrnl.exe 
6 ntoskrnl.exe IoGetBaseFileSystemDeviceObject + 0x7c8 0xfffff8015b8b8ae8 C:\WINDOWS\system32\ntoskrnl.exe 
7 ntoskrnl.exe PfFileInfoNotify + 0x6ead 0xfffff8015b8a823d C:\WINDOWS\system32\ntoskrnl.exe 
8 ntoskrnl.exe setjmpex + 0x224d 0xfffff8015b9dfdbd C:\WINDOWS\system32\ntoskrnl.exe 
9 ntoskrnl.exe memcpy + 0x250 0xfffff8015b9e2590 C:\WINDOWS\system32\ntoskrnl.exe 
10 ntoskrnl.exe MmMapLockedPagesSpecifyCache + 0x132e 0xfffff8015b89950e C:\WINDOWS\system32\ntoskrnl.exe 
11 ntoskrnl.exe MmMapLockedPagesSpecifyCache + 0x949 0xfffff8015b898b29 C:\WINDOWS\system32\ntoskrnl.exe 
12 ntoskrnl.exe CcCopyWriteEx + 0x1ca 0xfffff8015b965f9a C:\WINDOWS\system32\ntoskrnl.exe 
13 NTFS.sys NTFS.sys + 0xb7518 0xfffff8016f907518 C:\WINDOWS\System32\Drivers\NTFS.sys 
14 FLTMGR.SYS FltIsCallbackDataDirty + 0xb15 0xfffff8016e7f58b5 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
15 FLTMGR.SYS FltDecodeParameters + 0x3ad 0xfffff8016e7f2f1d C:\WINDOWS\System32\drivers\FLTMGR.SYS 
16 FLTMGR.SYS FltParseFileName + 0x159c 0xfffff8016e822eec C:\WINDOWS\System32\drivers\FLTMGR.SYS 
17 ntoskrnl.exe NtWriteFile + 0x432 0xfffff8015bca8532 C:\WINDOWS\system32\ntoskrnl.exe 
18 ntoskrnl.exe setjmpex + 0x37f3 0xfffff8015b9e1363 C:\WINDOWS\system32\ntoskrnl.exe 
19 ntdll.dll ZwWriteFile + 0xa 0x7ff9eb34357a C:\WINDOWS\SYSTEM32\ntdll.dll 
20 KERNELBASE.dll WriteFile + 0x88 0x7ff9e84cd458 C:\WINDOWS\system32\KERNELBASE.dll 
21 capture.exe capture.exe + 0x6f40b 0x7ff6b971f40b C:\ingest\server\capture.exe 
22 capture.exe capture.exe + 0x5998 0x7ff6b96b5998 C:\ingest\server\capture.exe 
23 capture.exe capture.exe + 0x13285 0x7ff6b96c3285 C:\ingest\server\capture.exe 
24 nxtcapture.exe nxtcapture.exe + 0x2b89 0x7ff6b96b2b89 C:\ingest\server\capture.exe 
25 capture.exe capture.exe + 0x136be1 0x7ff6b97e6be1 C:\ingest\server\capture.exe 
26 KERNEL32.DLL BaseThreadInitThunk + 0x22 0x7ff9eab02d92 C:\WINDOWS\system32\KERNEL32.DLL 
27 ntdll.dll RtlUserThreadStart + 0x34 0x7ff9eb2b9f64 C:\WINDOWS\SYSTEM32\ntdll.dll 

Le seguenti informazioni da CcCopyWriteEx potrebbe essere rilevante:

Se Wait è TRUE, CcCopyWriteEx è garantito per completare la copia richiesta e ritorno VERO. Se le pagine richieste del file memorizzato nella cache sono già residenti in memoria, i dati verranno copiati immediatamente e non si verificherà il blocco . Se le pagine necessarie non sono residenti, il chiamante verrà messo in stato di attesa finché tutte le pagine richieste non sono state rese residenti ei dati possono essere copiati.

Se ho capito bene questo funziona in modo simile a Mappatura della memoria in cui le pagine che vengono sovrascritti prima bisogno di leggere dal disco, anche se l'intera pagina è quello di essere sovrascritti. Un modo per evitarlo? Forse qualche Cache Manager Routine?

FILE_FLAG_WRITE_THROUGH fa la differenza. Si chiama ancora ReadFile ma non così spesso e la quantità letta dal disco sembra essere molto più bassa. Anche se non capisco perfettamente cosa sta succedendo e l'attività del disco e la lunghezza della coda sono ancora molto più elevate rispetto a quando si scrive su pagine non inizializzate nel file di destinazione.

0 FLTMGR.SYS FltDecodeParameters + 0x1ab1 0xfffff8018a9f4621 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
1 FLTMGR.SYS FltDecodeParameters + 0x166c 0xfffff8018a9f41dc C:\WINDOWS\System32\drivers\FLTMGR.SYS 
2 FLTMGR.SYS FltDecodeParameters + 0x1093 0xfffff8018a9f3c03 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
3 FLTMGR.SYS FltDecodeParameters + 0xe8e 0xfffff8018a9f39fe C:\WINDOWS\System32\drivers\FLTMGR.SYS 
4 ntoskrnl.exe IoPageRead + 0x258 0xfffff803f5e4d598 C:\WINDOWS\system32\ntoskrnl.exe 
5 ntoskrnl.exe IoPageRead + 0x4d4 0xfffff803f5e4d814 C:\WINDOWS\system32\ntoskrnl.exe 
6 ntoskrnl.exe IoGetBaseFileSystemDeviceObject + 0x7c8 0xfffff803f5e4bae8 C:\WINDOWS\system32\ntoskrnl.exe 
7 ntoskrnl.exe PfFileInfoNotify + 0x6ead 0xfffff803f5e3b23d C:\WINDOWS\system32\ntoskrnl.exe 
8 ntoskrnl.exe setjmpex + 0x224d 0xfffff803f5f72dbd C:\WINDOWS\system32\ntoskrnl.exe 
9 ntoskrnl.exe memcpy + 0x250 0xfffff803f5f75590 C:\WINDOWS\system32\ntoskrnl.exe 
10 ntoskrnl.exe MmMapLockedPagesSpecifyCache + 0x132e 0xfffff803f5e2c50e C:\WINDOWS\system32\ntoskrnl.exe 
11 ntoskrnl.exe MmMapLockedPagesSpecifyCache + 0x949 0xfffff803f5e2bb29 C:\WINDOWS\system32\ntoskrnl.exe 
12 ntoskrnl.exe CcCopyWriteEx + 0x1ca 0xfffff803f5ef8f9a C:\WINDOWS\system32\ntoskrnl.exe 
13 NTFS.sys NTFS.sys + 0x8ce8 0xfffff8018c068ce8 C:\WINDOWS\System32\Drivers\NTFS.sys 
14 NTFS.sys NTFS.sys + 0x7dc7 0xfffff8018c067dc7 C:\WINDOWS\System32\Drivers\NTFS.sys 
15 FLTMGR.SYS FltIsCallbackDataDirty + 0x424 0xfffff8018a9f51c4 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
16 FLTMGR.SYS FltDecodeParameters + 0xea6 0xfffff8018a9f3a16 C:\WINDOWS\System32\drivers\FLTMGR.SYS 
17 ntoskrnl.exe NtReadFile + 0xa1b 0xfffff803f623c72b C:\WINDOWS\system32\ntoskrnl.exe 
18 ntoskrnl.exe NtWriteFile + 0x680 0xfffff803f623b780 C:\WINDOWS\system32\ntoskrnl.exe 
19 ntoskrnl.exe setjmpex + 0x37f3 0xfffff803f5f74363 C:\WINDOWS\system32\ntoskrnl.exe 
20 ntdll.dll ZwWriteFile + 0xa 0x7ff9a313357a C:\WINDOWS\SYSTEM32\ntdll.dll 
21 KERNELBASE.dll WriteFile + 0x88 0x7ff9a059d458 C:\WINDOWS\system32\KERNELBASE.dll 
22 capture.exe capture.exe + 0x6f40b 0x7ff7eef0f40b C:\ingest\server\capture.exe 
23 capture.exe capture.exe + 0x5998 0x7ff7eeea5998 C:\ingest\server\capture.exe 
24 capture.exe capture.exe + 0x13285 0x7ff7eeeb3285 C:\ingest\server\capture.exe 
25 capture.exe capture.exe + 0x2b89 0x7ff7eeea2b89 C:\ingest\server\capture.exe 
26 capture.exe capture.exe + 0x136c71 0x7ff7eefd6c71 C:\ingest\server\capture.exe 
27 KERNEL32.DLL BaseThreadInitThunk + 0x22 0x7ff9a0a92d92 C:\WINDOWS\system32\KERNEL32.DLL 
28 ntdll.dll RtlUserThreadStart + 0x34 0x7ff9a30a9f64 C:\WINDOWS\SYSTEM32\ntdll.dll 

interessante anche con write-through è che sembra essere la lettura di singoli settori (nota Lunghezza: 4096 in ReadFile chiamate).

13:09:00,8579774 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 519 567 872, Length: 3 112 960, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:00,9399289 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 522 680 832, Length: 2 957 312, I/O Flags: Write Through, Priority: Normal 
13:09:00,9418288 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 522 680 832, Length: 2 957 312, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,0466551 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 525 638 144, Length: 3 145 728, I/O Flags: Write Through, Priority: Normal 
13:09:01,0486614 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 525 638 144, Length: 3 145 728, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,1476023 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 528 783 872, Length: 2 490 368, I/O Flags: Write Through, Priority: Normal 
13:09:01,1492754 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 528 783 872, Length: 2 490 368, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,2594166 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 531 274 240, Length: 2 981 888, I/O Flags: Write Through, Priority: Normal 
13:09:01,2613028 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 531 274 240, Length: 2 981 888, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,3693932 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 534 256 128, Length: 2 678 784, I/O Flags: Write Through, Priority: Normal 
13:09:01,3705444 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 534 256 128, Length: 90 112, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,3708446 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 534 346 240, Length: 2 588 672, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,4846832 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 536 934 912, Length: 3 096 576, I/O Flags: Write Through, Priority: Normal 
13:09:01,4862724 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 536 934 912, Length: 3 096 576, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,5905083 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 540 031 488, Length: 3 211 264, I/O Flags: Write Through, Priority: Normal 
13:09:01,5923326 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 540 031 488, Length: 3 211 264, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,6951367 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 543 242 752, Length: 2 670 592, I/O Flags: Write Through, Priority: Normal 
13:09:01,6967169 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 543 242 752, Length: 2 670 592, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,8028430 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 545 913 344, Length: 2 342 912, I/O Flags: Write Through, Priority: Normal 
13:09:01,8045821 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 545 913 344, Length: 2 342 912, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:01,9234657 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 548 256 256, Length: 3 055 616, I/O Flags: Write Through, Priority: Normal 
13:09:01,9254169 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 548 256 256, Length: 3 055 616, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,0273731 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 551 311 872, Length: 3 424 256, I/O Flags: Write Through, Priority: Normal 
13:09:02,0288307 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 551 311 872, Length: 3 424 256, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,1316979 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 554 736 128, Length: 2 678 784, I/O Flags: Write Through, Priority: Normal 
13:09:02,1327686 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 554 736 128, Length: 2 678 784, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,2327822 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 557 414 912, Length: 2 605 056, I/O Flags: Write Through, Priority: Normal 
13:09:02,2341425 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 557 414 912, Length: 2 605 056, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,3390269 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 560 019 968, Length: 2 711 552, I/O Flags: Write Through, Priority: Normal 
13:09:02,3402005 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 560 019 968, Length: 2 711 552, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,4392960 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 562 731 520, Length: 3 334 144, I/O Flags: Write Through, Priority: Normal 
13:09:02,4411620 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 562 731 520, Length: 3 334 144, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,5463951 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 566 065 664, Length: 2 277 376, I/O Flags: Write Through, Priority: Normal 
13:09:02,5474362 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 566 065 664, Length: 1 835 008, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,5484791 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 567 900 672, Length: 442 368, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,6509821 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 568 343 040, Length: 3 342 336, I/O Flags: Write Through, Priority: Normal 
13:09:02,6524223 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 568 343 040, Length: 3 342 336, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,7516238 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 571 685 376, Length: 2 555 904, I/O Flags: Write Through, Priority: Normal 
13:09:02,7529352 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 571 685 376, Length: 2 555 904, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,8526049 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 574 241 280, Length: 2 138 112, I/O Flags: Write Through, Priority: Normal 
13:09:02,8541937 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 574 241 280, Length: 2 138 112, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:02,9589201 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 576 379 392, Length: 3 039 232, I/O Flags: Write Through, Priority: Normal 
13:09:02,9602760 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 576 379 392, Length: 3 039 232, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,0738157 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 579 418 624, Length: 2 785 280, I/O Flags: Write Through, Priority: Normal 
13:09:03,0752279 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 579 418 624, Length: 2 785 280, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,1890830 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 582 203 904, Length: 3 383 296, I/O Flags: Write Through, Priority: Normal 
13:09:03,1908153 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 582 203 904, Length: 3 383 296, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,3075209 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 585 587 200, Length: 3 055 616, I/O Flags: Write Through, Priority: Normal 
13:09:03,3091505 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 585 587 200, Length: 3 055 616, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,4250265 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 588 642 816, Length: 3 006 464, I/O Flags: Write Through, Priority: Normal 
13:09:03,4266098 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 588 642 816, Length: 3 006 464, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,5379099 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 591 649 280, Length: 3 293 184, I/O Flags: Write Through, Priority: Normal 
13:09:03,5392216 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 591 649 280, Length: 3 293 184, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,6386064 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 594 942 464, Length: 2 596 864, I/O Flags: Write Through, Priority: Normal 
13:09:03,6403585 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 594 942 464, Length: 2 596 864, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,7476785 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 597 539 328, Length: 2 498 560, I/O Flags: Write Through, Priority: Normal 
13:09:03,7495491 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 597 539 328, Length: 2 498 560, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,8598891 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 600 037 888, Length: 3 522 560, I/O Flags: Write Through, Priority: Normal 
13:09:03,8613834 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 600 037 888, Length: 1 417 216, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,8622310 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 601 455 104, Length: 2 105 344, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:03,9748379 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 603 560 448, Length: 3 006 464, I/O Flags: Write Through, Priority: Normal 
13:09:03,9761048 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 603 560 448, Length: 3 006 464, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,0970842 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 606 566 912, Length: 3 104 768, I/O Flags: Write Through, Priority: Normal 
13:09:04,0986363 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 606 566 912, Length: 3 104 768, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,2026181 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 609 671 680, Length: 2 342 912, I/O Flags: Write Through, Priority: Normal 
13:09:04,2047880 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 839 040, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2059156 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 908 672, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2062328 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 912 768, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2124125 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 916 864, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2125033 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 920 960, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2125692 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 925 056, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2127042 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 929 152, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2130060 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 933 248, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2132903 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 610 937 344, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2134340 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 092 992, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2136517 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 097 088, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2139954 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 101 184, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2140859 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 105 280, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2142153 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 109 376, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2143550 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 113 472, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2144234 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 117 568, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2144772 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 611 121 664, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:04,2151351 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 609 671 680, Length: 2 342 912, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,3066104 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 612 014 592, Length: 2 940 928, I/O Flags: Write Through, Priority: Normal 
13:09:04,3085623 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 612 014 592, Length: 2 940 928, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,4154163 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 614 955 520, Length: 3 186 688, I/O Flags: Write Through, Priority: Normal 
13:09:04,4177492 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 614 955 520, Length: 3 186 688, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,5174478 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 618 142 208, Length: 2 547 712, I/O Flags: Write Through, Priority: Normal 
13:09:04,5192064 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 618 142 208, Length: 2 547 712, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,6315595 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 620 689 920, Length: 2 891 776, I/O Flags: Write Through, Priority: Normal 
13:09:04,6328619 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 620 689 920, Length: 2 891 776, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,7344473 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 623 581 696, Length: 3 055 616, I/O Flags: Write Through, Priority: Normal 
13:09:04,7358909 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 623 581 696, Length: 3 055 616, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,8373090 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 626 637 312, Length: 2 621 440, I/O Flags: Write Through, Priority: Normal 
13:09:04,8385106 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 626 637 312, Length: 2 621 440, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:04,9471593 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 629 258 752, Length: 3 047 424, I/O Flags: Write Through, Priority: Normal 
13:09:04,9485457 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 629 258 752, Length: 3 047 424, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:05,0705718 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 632 306 176, Length: 3 022 848, I/O Flags: Write Through, Priority: Normal 
13:09:05,0730288 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 632 306 176, Length: 2 703 360, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:05,0748379 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 635 009 536, Length: 319 488, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:05,1867648 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 635 329 024, Length: 3 383 296, I/O Flags: Write Through, Priority: Normal 
13:09:05,1885589 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 635 329 024, Length: 3 383 296, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:05,3091527 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 638 712 320, Length: 2 637 824, I/O Flags: Write Through, Priority: Normal 
13:09:05,3108466 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 638 712 320, Length: 2 637 824, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:05,4259338 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 641 350 144, Length: 3 506 176, I/O Flags: Write Through, Priority: Normal 
13:09:05,4277572 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 641 350 144, Length: 3 506 176, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Write Through, Priority: Normal 
13:09:05,5460495 capture.exe 3336 WriteFile L:\data.loop SUCCESS Offset: 1 927 644 856 320, Length: 3 309 568, I/O Flags: Write Through, Priority: Normal 
13:09:05,5479142 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 596 544, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5641906 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 633 408, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5679702 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 637 504, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5680940 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 641 600, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5684703 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 645 696, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5687985 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 649 792, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5688542 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 653 888, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5688983 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 657 984, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 
13:09:05,5692249 capture.exe 3336 ReadFile L:\data.loop SUCCESS Offset: 1 927 647 662 080, Length: 4 096, I/O Flags: Non-cached, Paging I/O, Synchronous Paging I/O, Priority: Normal 

Answer 1

Le letture che si stanno osservando molto probabilmente sono la cache del sistema operativo read-ahead. Il flag FILE_FLAG_WRITE_THROUGH è un'istruzione per il driver del disco su scrivere i dati direttamente per ignorare la cache del sistema hardware (anche se it is notoriously ignored by many less-than-enterprise-grade SATA drives). Questo flag non impedisce la memorizzazione nella cache dei dati da parte del sistema operativo o della cache del sistema del disco, né disabilita la cache del sistema operativo in lettura.

Suppongo che l'intenzione sia quella di scrivere il file ad alta velocità di trasmissione quasi continuamente e raramente, se mai, di leggerlo, come in un sistema di acquisizione di video o strumentazione. Lo è, quindi quello che stai cercando è un altro flag, FILE_FLAG_NO_BUFFERING, che disabilita sia il caching del sistema operativo dei dati dei file sia in lettura o scrittura. Ovviamente, read-ahead è disabilitato anche per soddisfare la promessa che le letture non provengono dalla cache di sistema.

Non specificareinsieme a FILE_FLAG_NO_BUFFERING a meno che non si desideri garantire che i dati siano stati effettivamente trasformati in bit magnetici dal momento in cui viene restituita la chiamata a WriteFile. Questo è inteso per l'elaborazione delle transazioni (come i server di database) e normalmente riduce le prestazioni di I/O del disco dell'applicazione, in alcuni casi di un fattore importante.