ZFS-REWRITE(8)

✨ zfs-rewrite 💅

okay bestie, welcome to zfs-rewrite — that's the manual page for the zfs rewrite command in the System Manager's Manual section. She's here to rewrite your files without changing a single byte of them and honestly? iconic behavior. 🎀

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🌸 NAME 🌸

zfs-rewrite — rewrite specified files without modification. no cap, the data stays exactly the same, it just gets a whole new lease on life. ✨

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🦋 SYNOPSIS 🦋

zfs rewrite [-Prvx] [-l length] [-o offset] file|directory…

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💖 DESCRIPTION 💖

So here's the tea: this command rewrites blocks of the file you point at as is, without modification, but at a new location, and possibly with new properties — like, imagine the file got atomically read and written back. glow up but make it byte-identical. 🫶

if you wanna know which properties can actually get applied during a rewrite, go read the “NOTES” section below, it's all in there. 👇

🎀 OPTIONS 🎀

• -P — perform a physical rewrite, preserving the logical birth time of blocks. by default, rewrite updates logical birth times, which makes blocks look modified in snapshots and incremental send streams. a physical rewrite keeps those logical birth times intact, so you avoid unnecessary inclusion in incremental streams. ⚠️ heads up though: physical rewrite requires the physical_rewrite feature to be enabled on the pool — no feature, no rewrite, periodt.
• -l length — rewrite at most this number of bytes. that's it, that's the whole vibe. 📏
• -o offset — start at this offset in bytes. like, where do we begin, bestie? 📍
• -r — recurse into directories. go down the whole tree, main character energy. 🌳
• -v — print the names of all successfully rewritten files. very "let me announce every W out loud". 🗣️
• -x — don't cross file system mount points when recursing. stay in your lane (affectionate). 🚧

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🔥 NOTES 🔥

okay this is the part you actually need, so like, pay attention. 👑

rewrite works by replacing an existing block with a new block of the same logical size. changed dataset properties that operate on the data or metadata without changing the logical size will be applied. that includes:

• checksum
• compression
• dedup
• copies

but bestie… changes to properties that affect the size of a logical block, like recordsize, will have no effect. she said no. 💀

rewrite of cloned blocks and blocks that are part of any snapshots — same as some property changes — may increase pool space usage. keep an eye on that. 👀

also: holes that were never written, or were previously zero-compressed, are not rewritten and will remain holes even if compression is disabled. a hole is a hole is a hole. 🕳️✨

and this one's lowkey important: if a -l or -o value requests a rewrite to regions past the end of the file, then those regions are silently ignored, and no error is reported. she just… doesn't mention it. 🙈

by default, rewritten blocks update their logical birth time, meaning they'll be included in incremental zfs send streams as modified data. when you use the -P flag though, rewritten blocks preserve their logical birth time, since there are no user data changes. slay. 💅

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🌈 SEE ALSO 🌈

• zfsprops(7)
• zpool-features(7)

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and that's the whole page, bestie!! 🥳 this was brought to you by OpenZFS, dated November 5, 2025 — go rewrite something, you absolute icon. 💜🦋🌸