1，Physical Disk vs. Logical Disk
Windows可以在一个Physical Disk上划出若干个逻辑分区，每一个逻辑分区是一个Logical Disk。对于分配在同一个Physical Disk上的Logical Disks，其读写操作共享Physical Disk的IO带宽。Windows给每一个Logical Disk分配一个盘符，App通过盘符来读写数据。
关于Disk Performance，有两组counter：Logical Disk 和 Physical Disk。Logical Disk Counter按照逻辑分区记录每个逻辑分区的读写IO信息，由于App通过盘符来读写数据，通过logical Disk Counter可以了解不同App向不同盘符发出的读写请求有多少。Physical Disk Counter是按照物理磁盘，记录每一个物理磁盘的读写IO,能够了解disk的响应速度。如果Physical Disk上划分多个Logical Disk，那么这些Logical Partition将作为一个整体统计。
The Physical Disk performance object monitors disk drives on the computer. It identifies the instances representing the physical hardware, and the counters are the sum of the access to all partitions on the physical instance.
The Logical Disk Performance object monitors logical partitions. Performance monitor identifies logical disks by their drive letter or mount point. If a physical disk contains multiple partitions, this counter will report the values just for the partition selected and not for the entire disk. On the other hand, when using Dynamic Disks the logical volumes may span more than one physical disk, in this scenario the counter values will include the access to the logical disk in all the physical disks it spans.
2, Disk Counter Explained
2.1 Disk Queue Length 是等待被Physical Disk处理的IO请求的数目。如果一个App发出一条读请求，但是目标Disk正在处理其他IO Task，那么这个新的请求就会被放在Disk queue中，Disk queue Length就是1.
Avg. Disk Queue Length ,Avg.Disk Read Queue Length,Avg.Disk Wirte Queue Length, Current Disk Queue length
2.2 Transfer 是Disk 的一次完整的I/O动作，表示从寻道，读写数据，到传输完成。在统计时，Transfer 是 Read 和 Write的加和。
Avg. Disk sec/Transfer ： 磁盘每一次读写所用的平均时间。
Disk Transfers/sec ： 磁盘每秒处理的读写次数。
Avg.Disk Bytes/Transfer：Disk 每次IO传送的Bytes数
2.3 Time percentage :Disk 处理IO请求和 elapsed time 的比值。
% Disk Time is the percentage of elapsed time that the selected disk drive was busy servicing write or read requests.
%Disk Time,% Disk Read Time,%Disk Write Time,%Idle Time
2.4 IO bytes
Avg. Disk Bytes/Read is the average number of bytes transferred from the disk during read operations.
Avg. Disk Bytes/Write is the average number of bytes transferred from the disk during write operations.
Avg. Disk Bytes/Transfer is the average number of bytes transferred to or from the disk during write or read operations.
Avg. Disk sec/Read is the average time, in seconds, of a read of data from the disk.
Avg. Disk sec/Transfer is the time, in seconds, of the average disk transfer.
Avg. Disk sec/Write is the average time, in seconds, of a write of data to the disk.
Disk Bytes/sec is the rate bytes are transferred to or from the disk during write or read operations.
Disk Read Bytes/sec is the rate at which bytes are transferred from the disk during read operations.
Disk Read Bytes/sec is the rate at which bytes are transferred from the disk during read operations.
Disk Reads/sec is the rate of read operations on the disk.
Disk Transfers/sec is the rate of read and write operations on the disk.
Disk Writes/sec is the rate of write operations on the disk.
2.5 IO Split，一次IO拆分成多次IO来实现
Measures the rate of IO split due to file fragmentation. This happens if the IO request touches data on non-contiguous file segments.
Split IO/Sec reports the rate at which I/Os to the disk were split into multiple I/Os. A split I/O may result from requesting data of a size that is too large to fit into a single I/O or that the disk is fragmented.
参考doc：
Windows Performance Monitor Disk Counters Explained