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本帖最后由 mark139 于 2011-9-18 13:02 编辑
per1-q1222 发表于 2011-9-18 08:12
Build策略就是所謂BGI...
這跟其他初始化策略不同..
BGI的目的只有一種..
关于这个初始化的问题, 还是有必要深入探讨一下的. 可能各个厂家的算法不太一样。我上Adaptec support Knowledge base找到了下面的Q&A:
Q:
What is the difference between Build / Verify, Clear, Quick Init and Skip Init when creating an array using one of the listed RAID controllers?
A:
Build / Verify
Array is available for use immediately. The Build operation continues in the background. Therefore, an operating system installation may begin while the array is going through the Build process, although performance will be impacted until the process has completed.
Creates parity/redundancy for each disk in the array. Example: For a RAID 1 logical drive, data is copied from the source drive to the mirrored drive. For RAID 5 and RAID 6, parity is computed and written.
A Build can take up to 20x longer than Clear (due to parity generation).
Clear
Array is not available to use until the operation completes.
Fastest way to set the disks into a known good state.
Writes only zeroes to the disk.
Although no real redundancy/parity is created, all disk sectors contain zeroes (no data) so none is required. Any future write operations will create required redundancy.
Quick Init
Array is available for use immediately.
Only creates metadata on member disks of the array, the build process is bypassed, the first few and last blocks in the user addressable area (incl. partition tables) will be wiped off. While this is the fastest method for creating a RAID array, it is only recommended for use with new drives. Performance will be impacted while the logical drive is in Quick Init mode until a Verify with Fix is performed from the Adaptec / ICP Storage Manager software.
For striped arrays (such as RAID 0, RAID 10, RAID 50, RAID 60), write performance is affected when less than a full stripe is written. The array remains in full-stripe write mode until a Verify with fix operation is completed to validate redundant information.
Default Setting for RAID 1, RAID 1EE, and RAID 10 arrays.
Skip Init
Updates metadata only.
If multiple disk drives fail in the same logical device, it may be possible to recover the data by recreating the logical device without the initialization step (skip init). Omitting the initialization step reconstructs the logical device metadata without modifying or destroying other data on the disks.
Not available on HostRAID (1220SA, 1225SA, 1420SA, 1430SA, 44300, 48300, 58300) controllers.
从上面可以了解到,采用“Clear”方式初始化,速度很快(本人的7T用时一分钟),初始化期间阵列不能使用,所有扇区写零,因无有效数据,无须也未作Parity计算,后期写入实际数据时,才会同时产生Parity值,没有提及会产生性能影响(如Build或Quick Init那样).
这个解释对我来说还是比较容易理解的。就像之前用ICH10R作Raid5初始化耗时87小时期间, 我一直纳闷,新盘上又没有任何有效数据,费这么大功夫去做全盘Read->Parity XOR->write有何意义?(难道当磁盘发生故障的时候,谁还想把未使用的空白部分也精准的恢复出来吗)像Adaptec这种快速清零的初始化做法无疑是明智之举 |
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