xfs_bmap(8)

💖 xfs_bmap(8) 💖

brought to you by the System Manager's Manual ✨

🎀 NAME 🎀

okay so xfs_bmap is the tool that prints the block mapping for an XFS file 🗺️ it basically shows you where a file's bytes actually live on disk, bestie 💅

🦋 SYNOPSIS 🦋

xfs_bmap [ -adelpv ] [ -n num_extents ] file
xfs_bmap -V

🌸 DESCRIPTION 🌸

okay so xfs_bmap prints the map of disk blocks that files in an XFS filesystem are using 🧠 the map lists every extent the file uses, and it also shows the gaps in the file that don't have any blocks behind them. those gaps are called holes 🕳️ each line of the output looks like this:

extent: [startoffset..endoffset]: startblock..endblock

if a region is a hole, the startblock..endblock part gets swapped out for the word hole 🙈 also, every file offset and disk block is measured in 512-byte blocks, no matter what block size your filesystem is using. the math is consistent, periodt ✨

👑 OPTIONS 👑

• -a — slide in with this and it shows the file's attribute fork instead of the usual data fork 💅
• -e — this one goes after all the delayed allocation extents 🧚 it doesn't flush dirty pages to disk before it looks at the extent data. if you also use -v, the flags column will tell you which extents still haven't been allocated 👀
• -l — adds a little tag to the end of every line that looks like this:

<nblocks>  blocks

nblocks is how long that extent is, counted in 512-byte blocks 📏 heads up though: if you're also using -v, this flag does absolutely nothing 💀

• -n num_extents — only shows you at most num_extents extents. if you leave this out, you get every single extent in the file 🫶
• -p — this one hunts down all the unwritten (preallocated) extents that don't have any written data in them 🌈 with -v, the flags column marks which extents are preallocated/unwritten ✨
• -v — verbose mode, bestie 🔍 it tacks some AG specific info onto each line in this format:

agno (startagoffset..endagoffset) nblocks flags

if you type -v a second time, you also get the flags legend 🏳️‍🌈

• -V — prints the version number and then bounces 👋

🧚 SEE ALSO 🧚

xfs_fsr(8), xfs(5) 💜

and that's the tea, bestie! 🍓 this was xfs_bmap(8) from the System Manager's Manual 🫶✨