4块磁盘做raid5 或 raid10，无缓存直接写入性能哪种方式更好？为此做了一个简单的测试对比，事实胜于雄辩，我们用实际测试数据来得出结论。
一、raid无缓存
3个文件系统：
---u01: hdd 4T*4 raid10，raid无缓存
---u02: hdd 4T*4 raid5，raid无缓存
---u03: ssd 447G*1
测试结果如下：
./testdd.sh /u01 /u02 /u03 > testdd.log.`date +%Y%m%d%H%M` 2>&1 &
vgraid10_local-lv01 7.3T 100G 7.2T 2% /u01 --- direct写入：38.7 MB/s direct读取：151 MB/s cache写入：328 MB/s cache读取：511 MB/s
vgraid5_local-lv01 11T 88G 11T 1% /u02 --- direct写入：7.4 MB/s direct读取：128 MB/s cache写入：77.6 MB/s cache读取：700 MB/s
vgssd_local-lv01 447G 65G 382G 15% /u03 --- direct写入：147 MB/s direct读取：189 MB/s cache写入：387 MB/s cache读取：512 MB/s
结论：
在无缓存（例如RAID卡禁用缓存、设置为Write Through模式，或使用无缓存的RAID卡）的情况下，针对4块磁盘的配置，RAID 10 的直接写入性能全面且大幅度地优于 RAID 5。
二、raid缓存模式
确认以上测试 u01/u02 是无缓存模式：
[root@host2 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdc 8:32 0 7.3T 0 disk
└─vgraid10_local-lv01 253:3 0 7.3T 0 lvm /u01
sdd 8:48 0 10.9T 0 disk
└─vgraid5_local-lv01 253:4 0 10.9T 0 lvm /u02
sdb 8:16 0 447.1G 0 disk
└─vgssd_local-lv01 253:5 0 447G 0 lvm /u03
执行 arcconf getconfig 1 ld 显示 Logical Device number 0 和 1 的配置信息：
[root@host2 ~]# arcconf getconfig 1 ld
Controllers found: 1
--------------------------------------------------------
Logical device information
--------------------------------------------------------
Logical Device number 0Logical Device name : vd1Disk Name : /dev/sdc (Disk0) (Bus: 1, Target: 0, Lun: 0)Block Size of member drives : 512 BytesArray : 0RAID level : 10Status of Logical Device : OptimalSize : 7630830 MBStripe-unit size : 256 KBFull Stripe Size : 512 KBInterface Type : Serial ATADevice Type : DataBoot Type : NoneHeads : 255Sectors Per Track : 32Cylinders : 65535Caching : DisabledMount Points : Not MountedLD Acceleration Method : NoneSED Encryption : DisabledVolume Unique Identifier : 600508B1001CF6173057FB8A85255004
--------------------------------------------------------Logical Device segment information
--------------------------------------------------------Segment : Availability (SizeMB, Protocol, Type, Connector ID, Location) Serial Number
--------------------------------------------------------Group 0, Segment 0 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:2) WQB0BYF0Group 0, Segment 1 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:4) WQB0B5PVGroup 1, Segment 0 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:3) WQB0B5V7Group 1, Segment 1 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:5) V302WXYFLogical Device number 1Logical Device name : vd2Disk Name : /dev/sdd (Disk0) (Bus: 1, Target: 0, Lun: 1)Block Size of member drives : 512 BytesArray : 1RAID level : 5Status of Logical Device : OptimalParity Initialization Status : CompletedSize : 11446245 MBStripe-unit size : 256 KBFull Stripe Size : 768 KBInterface Type : Serial ATADevice Type : DataBoot Type : NoneHeads : 255Sectors Per Track : 32Cylinders : 65535Caching : DisabledMount Points : Not MountedLD Acceleration Method : NoneSED Encryption : DisabledVolume Unique Identifier : 600508B1001CE4C11BEB914107DF0141
--------------------------------------------------------Array Physical Device Information
--------------------------------------------------------Device ID : Availability (SizeMB, Protocol, Type, Connector ID, Location) Serial Number
--------------------------------------------------------Device 14 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:6) V3039ZHFDevice 15 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:7) WQB0BY59Device 16 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:8) WQB0AW76Device 17 : Present (3815447MB, SATA, HDD, Connector:CN0, Enclosure:1, Slot:9) VB00EL3FCommand completed successfully.
关键信息是这两行：
Caching : Disabled
在 arcconf 设置 磁盘组的 Caching 为 WB 模式：
arcconf SETCACHE 1 LOGICALDRIVE 0 con
arcconf SETCACHE 1 LOGICALDRIVE 1 con
再次查询，已经强行改成了 缓存模式：
Caching : Enabled
再次测试磁盘的IO性能：
./testdd.sh /u01 /u02 > testdd.log.`date +%Y%m%d%H%M` 2>&1 &
vgraid10_local-lv01 7.3T 100G 7.2T 2% /u01 --- direct写入：38.3 MB/s direct读取：400 MB/s cache写入：303 MB/s cache读取：526 MB/s
vgraid5_local-lv01 11T 88G 11T 1% /u02 --- direct写入：7.1 MB/s direct读取：357 MB/s cache写入：33.7 MB/s cache读取：350 MB/s
结论：
打开RAID卡缓存后，raid5的 direct写入 性能仍然很差，但是 direct读取 性能有了大幅度提升！读取性能飙升而写入性能依旧拉胯，完全符合理论预期。
最后修改回原来设置：
因为 raid 卡无后备电池保护，存在丢数据风险。
arcconf SETCACHE 1 LOGICALDRIVE 0 coff
arcconf SETCACHE 1 LOGICALDRIVE 1 coff