Dell Perc5/i RAID5 读写优化

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Perc5/i(Dell™ PowerEdge™ Expandable RAID Controller 5/i)做RAID5的时候VD有Read Policy和Write Policy选项,但是没有发现Cache Policy. (RAID Controller Supported Features)
具体选项是:
Read Policy:
The read policies indicate whether or not the controller should read sequential sectors of the logical drive when seeking data.

  •  

Write Policy:The write policies specify whether the controller sends a write-request completion signal as soon as the data is in the cache or after it has been written to disk.

  • Write-Back. When using write-back caching, the controller sends a write-request completion signal as soon as the data is in the controller cache but has not yet been written to disk. Write-back caching may provide improved performance since subsequent read requests can more quickly retrieve data from the controller cache than they could from the disk. Write-back caching also entails a data security risk, however, since a system failure could prevent the data from being written to disk even though the controller has sent a write-request completion signal. In this case, data may be lost. Other applications may also experience problems when taking actions that assume the data is available on the disk.
  • Write-Through. When using write-through caching, the controller sends a write-request completion signal only after the data is written to the disk. Write-through caching provides better data security than write-back caching, since the system assumes the data is available only after it has been safely written to the disk.

缺少的Cache Policy选项是:
Cache Policy:
The Direct I/O and Cache I/O cache policies apply to reads on a specific virtual disk. These settings do not affect the read-ahead policy. The cache policies are as follows:

  • Cache I/O. Specifies that all reads are buffered in cache memory.
  • Direct I/O. Specifies that reads are not buffered in cache memory. When using direct I/O, data is transferred to the controller cache and the host system simultaneously during a read request. If a subsequent read request requires data from the same data block, it can be read directly from the controller cache. The direct I/O setting does not override the cache policy settings. Direct I/O is also the default setting.

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两台新上架的X3550 M2。在新机器基准测试的时候,发现磁盘性能比其它同类型机器的性能低很多。

检查发现PD,LD,BBU状态均正常。反馈到厂商那边,回复说需要把这个回写方式要改WriteThrough  为WriteBack。

改了之后,测试通过,前面几次测试都是差的,今天改了写入方式后,性能回到正常。话说之前换了几次RAID卡、硬盘, 浪费了很多时间

又,改这个可以直接用megacli命令去改。但有时候会修改不了。修改不了的时候需要进RAID设置界面那里去改。

# ./MegaCli32  LDSetProp WB -Lall -aALL

结论:电池present状态,并不代表RAID状态OK;比起看BBU状态,直接看Cache Policy更到位。

 

附:查看CaChe policy

# ./MegaCli ldPDinfo -a0 | grep -i write
Default Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Access Policy: Read/Write
Default Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Access Policy: Read/Write
Default Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAdaptive, Direct, No Write Cache if Bad BBU
Access Policy: Read/Write

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This page contains a single entry by suchasplus published on October 30, 2007 2:13 AM.

解决方案-Perc5i安装失败-错误代码:E1A15 was the previous entry in this blog.

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