Greg Freemyer wrote:
But with most setups barriers work and the journal can be relied on. ext4 defaults to metadata journaling, but not data journalling.
---- That's the difference between write-back (data done after journaled and after return success to user) vs. write-through (data is written through to disk , synchronously with the journal (and /or before returning to user, depending on usage context). The read cache has other requirements. I constantly see: [sda] Write cache: enabled, read cache: disabled, doesn't support DPO or FUA on some of my disks on bootup.
That means your filesystem structure is protected by barriers, but the content of your files is not. XFS for years was renowned for protecting files full of nulls for this reason.
I am pretty sure this wasn't the reason -- but had more to do with XFS's security requirement for Trusted Irix, which required, in-its-design, for files with "unwritten extents" to be marked as uninitialized -- so if they were mapped in the middle of a file, they'd be zero'd before being handed to the user. Conversely -- the opposite behavior, which wasn't as famous was seen on most other file systems -- having random garbage show up in a file -- that usually corresponded to a file fragment of some previously deleted file. Only in a minority of cases where such a file was a text file, would it be noted as "file data from a foreign file". Even then, unless it belongs to another user and contained something notable, someone might have thought it was text from one of their files that ended up as garbage in the middle of some other file...
That has been fixed in XFS as far as I know for 5+ years now.
Having used XFS on linux on work and home PC's since 2001, I'm pretty sure it was never the issue people think it was but was more the case of them not noticing equivalent cases of random-text in other file systems... unless those systems did 'write-through' which gives noticeably slow interactive performance. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org