constants.zig

/// The minimum size of an aligned kernel page and an Advanced Format disk sector:
/// This is necessary for direct I/O without the kernel having to fix unaligned pages with a copy.
/// The new Advanced Format sector size is backwards compatible with the old 512 byte sector size.
/// This should therefore never be less than 4 KiB to be future-proof when server disks are swapped.
pub const sector_size = 4096;

/// Whether to perform direct I/O to the underlying disk device:
/// This enables several performance optimizations:
/// * A memory copy to the kernel's page cache can be eliminated for reduced CPU utilization.
/// * I/O can be issued immediately to the disk device without buffering delay for improved latency.
/// This also enables several safety features:
/// * Disk data can be scrubbed to repair latent sector errors and checksum errors proactively.
/// * Fsync failures can be recovered from correctly.
/// WARNING: Disabling direct I/O is unsafe; the page cache cannot be trusted after an fsync error,
/// even after an application panic, since the kernel will mark dirty pages as clean, even
/// when they were never written to disk.
pub const direct_io = true;
pub const direct_io_required = true;