Pierre-Philipp Braun <pbraun%nethence.com@localhost> writes: > here's a little but not necessarily simple question. It's noted in > the official RAIDframe guide that one should disable disk _write_ > caching if there is no Uninterruptible Power Supply installation. I find it surprising that this is in the raidrame guide. There are two issues: write caching on disks is unsafe, unless there is a guarantee that anything acknowledged by the disk will make it to stable storage even if there is a power failure. Typically this involves UPS or battery-backed ram cache on the disk controller (in high-end hardware raid controllers). RAID5 in software is scary, because it involves read-modify-write cycles of stripes that involve logical blocks that are not being written. Or perhaps RAID5 without battery-backed caches is scary. I have dealt with this by only using RAID1. The first issue about has nothing to do with raidframe. With RAID1, I'm not aware of extra considerations for raidframe RAIS1 vs just using a disk. > Ok. Now what happens if there is a kernel panic? (Yep, this can > happen.) Technically, wouldn't it be the same issue? A panic should result in long enough time between the last write to the disk (sent to the controller) and the reset from the reboot for the data to all be written. In theory writes are ordered such that corruption will not occur, even though individual files in the process of being written may have incorrect data blocks.
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