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yangyang 取决于你是不是SquashFS 
 SquashFS is a read only compressed filesystem. While gzip is available, at OpenWrt it uses LZMA for the compression. Since SquashFS is a read only filesystem, it doesn't need to align the data, allowing it to pack the files tighter thus taking up significantly less space than JFFS2 (20-30% savings over a JFFS2 filesystem)!
    + taking up as little space as possible
    + allowing the implementation of an idiot proof FailSafe for recovery, since it is not possible to write to it
    - read only
    - waste space, since each time a file contained on it is modified, actually a copy of it is being copied to the second (JFFS2) partition
你的可能不是squashfs,输条mount来看看?