scsi中DPO和FUA 是什么

最新推荐文章于 2025-09-18 14:05:22 发布

转载最新推荐文章于 2025-09-18 14:05:22 发布 · 1.1w 阅读

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#server #cache #access #application

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本文介绍了SCSI标准中关于缓存控制的概念，包括DPO（禁止换出）和FUA（强制单元访问）。详细解释了这两种机制如何影响读写操作，并说明了当两者同时启用时，读写操作将直接绕过缓存。

做硬盘驱动遇到
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
没时间细读总线规范(SCSI Block Commands-2)的话，以下是简介
DPO是disable page out的缩写,FUA是force unit access的缩写.
When the cache becomes full of logical blocks, new logical blocks may replace those currently in the cache. The disable page out (DPO) bit in the CDB of commands performing write, read, or verify operations allows the application client to influence the replacement of logical blocks in the cache. For write operations, setting the DPO bit to one specifies that the device server should not replace existing logical blocks in the cache with the new logical blocks being written. For read and verify operations, setting the DPO bit to one specifies that the device server should not replace logical blocks in the cache with the logical blocks that are being read.
Application clients may use the force unit access (FUA) bit in the CDB of commands performing write or read operations to specify that the device server shall access the medium. For a write operation, setting the FUA bit to one causes the device server to complete the data write to the medium before completing the command. For a read operation, setting the FUA bit to one causes the device server to retrieve the logical blocks from the medium rather than from the cache.
When the DPO and FUA bits are both set to one, write and read operations effectively bypass the cache.