Read Policy, Write Policy가 있는데 IO Policy가 따로 있는 이유는 뭔가요?
아래 영문 메뉴얼봐도 딱히 이해가 안됩니다.
IO Policy에서 말하는 specific virtual drive라는게 어떤것을 말하는 것인지도 모르겠고요,
IO Policy라고 하면서 왜 Read에 관련된 설정값만 있는것인지도 의문 입니다..-_-;
참고로 리눅스서버의 dmesg에서 "Write cache"값을 보면...
Read Policy의 값을 Always Read Ahead로 했을때도 Read cache : enable 이고
IO Policy의 값을 Cached로 했을때도 Read cache : enable 로 나오네요.
-_-;;;
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Access Policy: Select the type of data access that is allowed for this virtual drive.
? RW: Allow read/write access. This is the default.
? Read Only: Allow read-only access.
? Blocked: Do not allow access.
Read Policy: Specify the read policy for this virtual drive.
? No Read Ahead: This option disables the read ahead capability. This option is the default.
? Always Read Ahead: This option enables read ahead capability, which allows the controller to read
sequentially ahead of requested data and to store the additional data in cache memory, anticipating that the
data will be needed soon. This option speeds up reads for sequential data, but there is little improvement
when accessing random data.
Write Policy: Specify the write policy for this virtual drive.
? Always Write Back: In Write back mode, the controller sends a data transfer completion signal to the host
when the controller cache has received all of the data in a transaction. This setting is recommended in
Standard mode.
? Write Through: In Write through mode, the controller sends a data transfer completion signal to the host
when the drive subsystem has received all of the data in a transaction. This option is the default setting.
? Write Back with BBU: Select this mode if you want the controller to use Write back mode but the controller
has no BBU or the BBU is bad. If you do choose this option, the controller firmware automatically switches to
Write Through mode if it detects a bad or missing BBU.
IO Policy: The I/O policy applies to reads on a specific virtual drive. It does not affect the read ahead cache.
? Direct: In Direct I/O mode, reads are not buffered in cache memory. Data is transferred to the cache and the
host concurrently. If the same data block is read again, it comes from cache memory. This option is the
default setting.
? Cached: In Cached I/O mode, all reads are buffered in cache memory.
Drive Cache: Specify the drive cache policy.
? Enable: Enable the drive cache.
? Disable: Disable the drive cache. This option is the default setting.
? Unchanged: Leave the current drive cache policy as is.
Disable BGI: Specify the Background Initialization (BGI) status.
? No: Leave background initialization enabled, which means that a new configuration can be initialized in the
background while you use WebBIOS to perform other configuration tasks. This option is the default setting.
? Yes: Select Yes if you do not want to allow background initializations for configurations on this controller.
OS Admin
디스크의 어떤 부분을 읽을 때, 그 다음부분도 미리 읽어서 캐쉬할 것인지에 대한 설정입니다.
그래서 순차읽기를 할 때 Read Ahead 캐쉬를 크게 잡으면 성능 향상이 있습니다.
Direct I/O와 Cached I/O는... 저도 올려주신 그 설명은 이해가 잘 안가지만, 일반적으로 이런 개념은 DB나 파일입출력에서 사용할 때에, Direct I/O는 대상을 직접 접근해서 읽어 오는 방식이고, 반면에 Cached I/O는 캐쉬쪽에 읽기 요청을 하고, 캐쉬 컨트롤러에서 I/O를 수행한 다음에 전달하는 방식입니다.
보통 Latency 쪽은 Direct I/O가 좋을 것이고요, Throughput은 Cached I/O쪽이 좋겠지요.