diff --git a/en_US.ISO8859-1/books/arch-handbook/driverbasics/chapter.sgml b/en_US.ISO8859-1/books/arch-handbook/driverbasics/chapter.sgml index dbbd2c7ebf..b017856fae 100644 --- a/en_US.ISO8859-1/books/arch-handbook/driverbasics/chapter.sgml +++ b/en_US.ISO8859-1/books/arch-handbook/driverbasics/chapter.sgml @@ -527,6 +527,33 @@ Test Data + + Block Devices (Are Gone) + + Other &unix; systems may support a second type of disk + device known as block devices. Block devices are disk devices + for which the kernel provides caching. This caching makes + block-devices almost unusable, or at least dangerously + unreliable. The caching will reorder the sequence of write + operations, depriving the application of the ability to know + the exact disk contents at any one instant in time. This + makes predictable and reliable crash recovery of on-disk data + structures (filesystems, databases etc.) impossible. + Since writes may be delayed, there is no way the kernel can + report to the application which particular write operation + encountered a write error, this further compounds the + consistency problem. For this reason, no serious applications + rely on block devices, and in fact, almost all applications + which access disks directly take great pains to specify that + character (or raw) devices should always be + used. Because the implementation of the aliasing of each disk + (partition) to two devices with different semantics significantly + complicated the relevant kernel code &os; dropped support for + cached disk devices as part of the modernization of the disk I/O + infrastructure. + + + Network Drivers