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I'm experimenting with using btrfs on my Debian Linux armhf system. The rfs is on a micro SD card. On bootup I get the message "Btrfs detected SSD devices, enabling SSD mode". What features does this SSD mode give me exactly?

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Traditional hard drives have a spinning disk platter. This means that filesystems can (and do) perform several optimizations. For example, it will locate segments of a file in a contiguous region of the disk, so that when you read different parts of the file, the kernel doesn't have to wait for the platter to spin to a different place. Another optimization done is to locate often-accessed files near each other. Again, this means that statistically, you will spend less time waiting for the disk platter to turn.

By definition, a solid-state drive doesn't have a spinning platter. This means that all of the optimizations done for spinning-platter devices are a dumb idea. All that SSD mode does is turn these optimizations off. Nothing to worry about.

  • OK that is good to know. Do you happen to know what exactly happens when there's a checksum error when doing a read? From what I've read an error is logged, but is this returned to the calling application somehow? On my systems there is no human to read the logs. – fred basset Jun 2 '14 at 3:44
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    Platters spin all the time and don't move. That's the disk head that needs to move upon a seek instead of reading what's just there. – Stéphane Chazelas Jun 2 '14 at 6:19
  • @fredbasset ask a new question. – strugee Jun 2 '14 at 7:40
  • @StéphaneChazelas thanks for the correction; I'll update it in the morning – strugee Jun 2 '14 at 7:41

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