* volume server: open volume files with O_NOATIME
Nothing reads the atime of .dat, .idx, .sdx, or EC files, but every
needle read still dirtied the inode: even relatime writes atime on the
first read after each write, so an actively written volume paid a
metadata write per read/write cycle, and strictatime mounts paid one
per read. Open the serving handles with O_NOATIME, falling back to a
plain open when the file belongs to another owner (EPERM).
Claude-Session: https://claude.ai/code/session_015uVY4diBgEn3VYQoc2eMuD
* seaweed-volume: mirror the O_NOATIME volume file opens
Same change as the Go volume server: serving handles for .dat, .idx,
.sdx, .ecx, .ecj, and shard files open with O_NOATIME on Linux, with a
plain-open fallback on EPERM.
Claude-Session: https://claude.ai/code/session_015uVY4diBgEn3VYQoc2eMuD
* route the tier-down and recreate .dat opens through the no-atime helper
Review caught the Rust tier-down swap opening the local .dat directly.
The Go swapToLocalDatBackend and the zero-length read-only .dat
recreate in maybeWriteSuperBlock had the same gap: all three install
long-lived serving handles.
Claude-Session: https://claude.ai/code/session_015uVY4diBgEn3VYQoc2eMuD
