LCTL-BARRIER(8)

💖 LCTL-BARRIER(8) 💖

okay bestie, welcome to lctl-barrier, aka the Lustre write barrier utilities, from the Lustre Configuration Utilities corner of the universe. if you've ever wanted to ✨pause✨ all the metadata drama on your filesystem and then let it breathe again, this is the page for you. no cap.

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✨ SYNOPSIS ✨

lctl barrier_freeze FSNAME [TIMEOUT]
lctl barrier_thaw FSNAME
lctl barrier_stat [--state|-s] [--timeout|-t] FSNAME
lctl barrier_rescan FSNAME [TIMEOUT]

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🌸 DESCRIPTION 🌸

🧊 barrier_freeze FSNAME [TIMEOUT]

bestie, this one sets the write barrier on all MDTs. and like — it does not come back until the barrier is actually set (frozen) or it flat out fails. no half-measures, we wait. 💅

once the write barrier is set, every subsequent metadata modification gets blocked until the barrier is thawed or it expires. the barrier lifetime starts ticking the moment you trigger the freeze, and it ends when the barrier gets thawed.

now, because nobody wants the whole system frozen forever just because you missed or failed to call barrier_thaw (rip), you can set how long it lives with the TIMEOUT parameter, in seconds. the default is 30 (seconds), periodt. if the barrier isn't thawed before that, it expires automatically. iconic self-preservation tbh.

heads up: this command can only succeed when all registered MDTs are available. if some MDT is registered but goes offline, the freeze command will just fail. to check and update the current status of MDTs, go look at barrier_rescan in the section right below, iykyk. 🫶

🦋 barrier_thaw FSNAME

reset the write barrier on all MDTs. once the write barrier is thawed, all those blocked metadata modifications (yes, the ones from that earlier barrier_freeze, they've been waiting so patiently 😭) get handled normally again. the vibe returns. 🌈

⭐ barrier_stat [--state|-s] [--timeout|-t] FSNAME

query the write barrier status, bestie. here are all the possible statuses and what they mean:

• init: has never set barrier on the system
• freezing_p1: in the first stage of setting the write barrier
• freezing_p2: in the second stage of setting the write barrier
• frozen: the write barrier has been set successfully
• thawing: in thawing the write barrier
• thawed: the write barrier has been thawed
• failed: fail to set write barrier
• expired: the write barrier is expired
• rescan: in scanning the MDTs status, see the command barrier_rescan
• unknown: other cases

if the barrier is in freezing_p1, freezing_p2 or frozen status, then the lifetime remaining gets returned too. 👑

if no option is specified, or if both -s and -t options are specified, the output format is:

state: xxx
timeout: nnn seconds

otherwise, only the value (xxx or nnn) corresponding to the given option gets printed. one value, no extra vibes.

🧚 barrier_rescan FSNAME [TIMEOUT]

scan the system to check which MDTs are active. why do we care, you ask? because barrier_freeze will be unsuccessful if any of the MDTs are permanently offline. 💀 during the rescan, the MDT status gets updated.

if an MDT doesn't respond to the barrier_rescan within the given TIMEOUT seconds (default is 30 seconds, same energy as before), then it gets marked as unavailable or inactive. sorry babe, you're benched.

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💜 AVAILABILITY 💜

lctl-barrier is part of the lustre(7) filesystem package since release 2.10.0. she's been here a minute. 🌟

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👑 SEE ALSO 👑

• lctl(8)
• lctl-snapshot-create(8)

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okay that's the whole page, bestie, hope it slayed 🎀 — this gorgeous piece of Lustre documentation comes to you from the Lustre crew, dated 2024-08-13, and it lives under the name LCTL-BARRIER(8). bye pookie, go thaw something 💖