LDEV.CONF(5)

💖 LDEV.CONF(5) 💖

okay bestie, welcome to the Lustre File Formats corner of the manual, section 5 💅 this one's all about /etc/ldev.conf — the lustre device configuration file. grab a strawberry drink 🍓 and let's go.

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✨ NAME ✨

/etc/ldev.conf — the lustre device configuration file 🎀

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🌸 DESCRIPTION 🌸

so basically, the ldev.conf file is a whole list of Lustre devices that the ldev utility uses. that's it, that's the vibe. 💜

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🦋 FORMAT 🦋

okay so the formatting rules, listen up:

• comments that start with a hash (#) are ignored, no cap. they're just there for the vibes.
• every single line = one device. and each line carries the following info, all separated by a white space:

now the fields, in order, here we goooo:

• LOCAL_HOSTNAME — the name of the host where the device normally runs. its home base, its main character location 👑
• FOREIGN_HOSTNAME — the name of the host where the device runs when it gets failed over. if failover isn't a thing for you, just drop a hyphen in as a placeholder. it's giving "no backup host, no problem" 💁
• LABEL — the Lustre label tied to the device, and it has to be in the form FSNAME-{OST|MDT}NNNN where FSNAME is the file system name, then either OST or MDT, and NNNN is the four-digit hex index of the device. yes, hex. NNNN is literally hexadecimal, don't come for me 🔢
• DEVICE_PATH — the path name of the device. heads up: in failover configurations this needs to be available on both the local and the foreign hosts, so like… use the symlinks that udev maintains in /dev/disk/by-id. that's the move, trust 🫶
• JOURNAL_PATH — the path name of the journal device, if there even is one. this field can be omitted, unless the raidtab field is present. and if you're not using a journal device, you can just put a hyphen as a placeholder instead. either way works ✨
• RAIDTAB — the path name of a Linux software raid configuration file, or a ZFS cache file. lowkey the tea here: using non-default names for these files may help prevent arrays from being automatically started by the system. and this is important in failover configurations where the timing of device initialization has to be strictly controlled. timing is everything, periodt ⏰ this field may be omitted.

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🔥 EXAMPLES 🔥

first up, ldiskfs on a block device, iconic behaviour:

# ldiskfs on block device example
# LOCAL FOREIGN/- LABEL [md:|zfs:]DEVICE_PATH [JOURNAL_PATH]/- [RAIDTAB]
tycho-mds1 -    lc1-MDT0000 /dev/sda                /dev/sdc
tycho1  tycho5  lc1-OST0000 /dev/disk/by-id/scsi-10103a262891d340100
tycho1  tycho5  lc1-OST0008 /dev/disk/by-id/scsi-10103a262681d340200
tycho1  tycho5  lc1-OST0010 /dev/disk/by-id/scsi-10103a2629e1d340300
tycho5  tycho1  lc1-OST0004 /dev/disk/by-id/scsi-101046e6b401d341100
tycho5  tycho1  lc1-OST000c /dev/disk/by-id/scsi-101046e6b591d341200
tycho5  tycho1  lc1-OST0014 /dev/disk/by-id/scsi-101046e6bb41d341300

then ldiskfs on Linux software RAID, also slay:

# ldiskfs on Linux software RAID example
# LOCAL FOREIGN/- LABEL [md:|zfs:]DEVICE_PATH [JOURNAL_PATH]/- [RAIDTAB]
zwicky-mds1  -    zwicky-MDT0000 md:/dev/md0 -         /etc/mdadm.conf.mds
zwicky1  zwicky2  zwicky-OST0000 md:/dev/md0 /dev/md10 /etc/mdadm.conf.oss
zwicky2  zwicky1  zwicky-OST0001 md:/dev/md1 /dev/md20 /etc/mdadm.conf.oss

aaaaand ZFS, because we contain multitudes 🧚:

# ZFS example
# LOCAL FOREIGN/- LABEL [md:|zfs:]DEVICE_PATH [JOURNAL_PATH]/- [RAIDTAB]
zeno-mds1 -   zeno-MDT0000 zfs:lustre-zeno-mds1/mdt1 - /etc/zfs/zpool.cache.zeno
zeno1  zeno5  zeno-OST0000 zfs:lustre-zeno1/ost1     - /etc/zfs/zpool.cache.zeno
zeno5  zeno1  zeno-OST0001 zfs:lustre-zeno5/ost1     - /etc/zfs/zpool.cache.zeno

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🌈 AVAILABILITY 🌈

/etc/ldev.conf has been part of the lustre(7) filesystem package since release 2.3.0. vintage, but make it cute 💖

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⭐ SEE ALSO ⭐

• ldev(8) — go read it, it's literally right there bestie

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and that's the whole page!! mwah 😚 this lovely little writeup is from the Lustre manual, dated 2024-08-29. stay configured, stay iconic 👑✨