Hector Martin

PSA PSA PSA: if you use LVM with USB drives you will get absolutely *abysmal* performance by default (especially on HDDs). You must use `pvcreate --dataalignment 2048s` to fix it. Fix requires re-creating PV and copying all data.

Seriously, on most current drives (512e) random write performance will be *abso-fucking-lutely atrocious* unless you fix this, and SSDs will have increased wear.

This happens because the USB drive maximum transfer size is 65535 sectors, and LVM in its infinite wisdom decides that's a good alignment value for PVs, thus de-aligning the physical sectors/FS blocks completely, causing read-modify-write cycles for every single small write.

Apparently querying /sys/block/$disk/queue/physical_block_size was too hard??