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btrfs-progs: docs: update memory related problems

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Inspired by https://www.reddit.com/r/btrfs/comments/1bkdewb/btrfs_errors_in_dmesg/ .

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Signed-off-by: David Sterba <dsterba@suse.com>
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David Sterba 2024-03-25 23:29:01 +01:00
parent 2c99d8078f
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Documentation/ch-hardware-considerations.rst
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@ -118,9 +118,21 @@ have been demonstrated (*rowhammer*) achieving specific bits to be flipped.
While these were targeted, this shows that a series of reads or writes can
affect unrelated parts of memory.
Block group profiles with redundancy (like RAID1) will not protect against
memory errors as the blocks are first stored in memory before they are written
to the devices from the same source.
A filesystem mounted read-only will not affect the underlying block device in
almost 100% (with highly unlikely exceptions). The exception is a tree-log that
needs to be replayed during mount (and before the read-only mount takes place),
working memory is needed for that and that can be affected by bit flips.
There's a theoretical case where bit flip changes the filesystem status from
read-only to read-write.
Further reading:
* https://en.wikipedia.org/wiki/Row_hammer
* memory overclocking, XMP, potential risks
What to do:
@ -129,6 +141,9 @@ What to do:
* memory errors may appear as filesystem going read-only due to "pre write"
check, that verify meta data before they get written but fail some basic
consistency checks
* newly built systems should be tested before being put to production use,
ideally start a IO/CPU load that will be run on such system later; namely
systems that will utilize overclocking or special performance features
Direct memory access (DMA)
^^^^^^^^^^^^^^^^^^^^^^^^^^