Matthias Schniedermeyer wrote:
> For the filesystem any block device looks the same, regardless if it is a
> HDD, FDD, a(n encrypted-)loop or whatever else is used to satisfy the
> issued requests.
Actually block devices have differences that file systems have to deal with:
1) Hard sector sizes may be different. File system code must detect block
device hard sector size and avoid issuing partial sector accesses.
2) Some device drivers don't support variable length read/write requests.
XFS for example had (has?) list of 'problematic' devices that needed
fixed size read/write requests. IIRC, md raid on 2.4 kernels was such
block device that got upset when banged with variable length requests.
3) Some block devices support write barriers on 2.6 kernels, some don't.
A file system that wants to issue barrier write requests have to work
around the not supported cases.
4) Maximum request sizes and bunch of other limits may be different.
--
Jari Ruusu 1024R/3A220F51 5B 4B F9 BB D3 3F 52 E9 DB 1D EB E3 24 0E A9 DD
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Linux-crypto: cryptography in and on the Linux system
Archive: http://mail.nl.linux.org/linux-crypto/
