Physical Storage¶
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Overview¶
- 三级存储 offline storage
- optical disk 光学存储器 CD
- tape disk 磁带
访问必须从头开始，顺序访问
Flash Memory | 闪存¶
NOR快闪
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可以访问单个字
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速度可以与主存媲美
NAND快闪 SSD
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Reading from NAND flash requires an entire page of data, which is very commonly 4096 bytes, to be fetched from NAND flash into main memory.
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更经常用的
闪存特点
- 写操作比较复杂，一旦完成写操作，想要复写必须擦除之后再写
- The erase operation must be performed on a group of pages, called an erase block
- 容易损坏 Further, there is a limit to how many times a flash page can be erased, typically around 100,000 to 1,000,000 times. Once this limit is reached, errors in storing bits are likely to occur.
Magnetic Disk¶
- 通过机械运动，比较慢
- 扇区是最小的读写单元
Performance¶
- 上面的IOPS支持的操作是Random的R/W
Optimization¶
