(thanks for the ref to the neu.edu paper, I hadn't read that.) On Sep 24, 2013, at 6:07 PM, Stefan Monnier wrote:
> - I've found USB flash disks to be reasonably reliable in general, but > one case where I've had trouble is when disconnecting the key while > the system is writing to it. That can lead to severe corruption > (despite use of things like logging file-systems). I've seen that, except without the disconnect. USB Flash disks have no consistency/atomicity guarantees, at all. If there is a failure of any sort, it may result in "impossible" filesystem contents, and fsck.ext3 may be extremely confused. Many consumer flash drives are optimized for a FAT and may have different commit behavior for blocks below and above the (say) 4M mark. I stopped trying to run 24/7 systems with / on USB Flash about five years ago. Things *may* have improved since then, but I wouldn't know.... If you can live with a livecd-like cramfs overlay, that might work pretty well. Just be prepared to lose the overlay filesystem, or anything else you touch frequently. If somebody held a gun to my head and said "build me a reliable system" I would probably keep tgz snapshots of /overlay on a FAT filesystem; on boot, I would restore the last one with a good checksum. Some people say "don't ever reformat" because of alignment issues etc, but it's probably safe to shrink the main FAT filesystem and keep the cramfs on a separate partition at the end of the drive. If USB ports are not a problem, using a second drive might help a lot. The standard performance disaster is demand-loading an executable from /usr/bin while the (queue-depth 0) disk is frozen with 10IOPS writes to /var/log or $HOME/.browsercache/. Jay _______________________________________________ openwrt-users mailing list [email protected] https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-users
