为什么英特尔 RST RAID 1 阵列在禁用回写缓存的情况下写入速度更快？

Question

我在 RAID 1（镜像）中有两个 HDD (5900 RPM)。我知道，我知道，这太慢了。我目前正在用更快的驱动器替换它们，因此在我测试时出现了这个问题。

出于某种原因，在英特尔 RST 选项中禁用回写缓存可以让我获得更快的写入速度，反之亦然。据我所知，如果禁用回写缓存，我希望写入速度会降低。那是对的吗？这只是监控程序中的错误吗？

缓存已启用：

缓存禁用：

英特尔 RST 系统报告：

System Report

System Information
OS name:  Microsoft Windows 7 Professional 
OS version:  6.1.7601 Service Pack 1 7601
System name:  (redacted)
System manufacturer:  MSI
System model:  MS-7673
Processor:  GenuineIntel Intel64 Family 6 Model 42 Stepping 7 3.401  GHz
BIOS:  BIOS Date: 08/01/12 15:53:14 Ver: 04.06.04, ALASKA - 1072009

Intel® Rapid Storage Technology
Kit installed:  10.5.0.1007
User interface version:  10.5.0.1007
Language:  English (Australia)
Intel RAID controller:  Intel(R) Desktop/Workstation/Server Express Chipset SATA RAID Controller
Number of SATA ports:  6
RAID option ROM version:  10.5.0.1034
Driver version:  10.5.0.1007
ISDI version:  10.5.0.1007

Device Information
Name:  Array_0000
Size:  3.6 TB
Available space:  0 GB
Disk data cache:  Enabled
Number of volumes:  1
Volume member:  OS
Number of disks:  2
Array disk:  5YD2V3WZ
Array disk:  5YD2VEPK

Name:  OS
Status:  Normal
Type:  RAID 1
Size:  1.8 TB
Data stripe size:  64 KB
Write-back cache:  Enabled
System volume:  Yes  
Initialized:  Yes  
Verification errors found:  72
Blocks with media errors:  0
Physical sector size:  512 Bytes
Logical sector size:  512 Bytes
Parent array:  Array_0000
Number of disks:  2
Array disk:  5YD2V3WZ
Array disk:  5YD2VEPK

Disk on port 0
Port location:  Internal
Status:  Normal
Type:  Hard disk
Usage:  Array disk
Size:  1.8 TB
Serial number:  5YD2V3WZ
Model:  ST2000DL003-9VT166
Firmware:  CC32
System disk:  No
Password protected:  No
Disk data cache:  Enabled
Native command queuing:  Yes  
SATA transfer rate:  6 Gb/s
Physical sector size:  512 Bytes
Logical sector size:  512 Bytes

Disk on port 1
Port location:  Internal
Status:  Normal
Type:  Hard disk
Usage:  Array disk
Size:  1.8 TB
Serial number:  5YD2VEPK
Model:  ST2000DL003-9VT166
Firmware:  CC32
System disk:  No
Password protected:  No
Disk data cache:  Enabled
Native command queuing:  Yes  
SATA transfer rate:  6 Gb/s
Physical sector size:  512 Bytes
Logical sector size:  512 Bytes

(redacted other disks)

Answer 1

在回写式缓存中，当控制器缓存接收到事务中的所有数据时，控制器向主机发送数据传输完成信号。

在直写式缓存中，当磁盘子系统接收到事务中的所有数据时，控制器向主机发送数据传输完成信号。

回写式缓存有以下缺点：

• 如果要替换块，则仅在设置了更新位时才写入主存储器
• I/O必须通过缓存访问主存

参考

• 缓存写入策略和性能(pdf)

• 配置和管理 RAID：CERC 6/i 用户指南

• 直写式缓存