Public bug reported:
Using: Ubuntu 21.10 and OpenZFS 2.0. I did the standard ZFS install of Ubuntu.
I had terrible bad response times from my brand new 2 TB Seagate STM2000M007
HDD, sometimes it takes 5 seconds or so to start the terminal and the system
boots in 4 minutes from the HDD. I installed Ubuntu 21.04 on OpenZFS 2.0.2 and
upgrade to Ubuntu 21.10 on OpenZFS 2.0.6 and both combinations on that HDD did
cause that awful performance. It is a normal laptop drive at 5400 rpm. Its
sequential read/write speeds are ~140MB/s while its seek times are ~13 msec.
The measurement with gnome disk utility confirmed those values from the
specification, the throughput on ZFS was ~120MB/s, but the difference
could be caused by the latency of the 10 year old i5-2520M (2C4T;
2.5/3.2GHz). The disk SMART data was OK.
Everything seems normal, ashift is set to 12 and the HDD has 4096 Byte
physical sectors and 512 Byte logical sectors. All partitions are
starting on 2048 boundaries of UEFI. I had been thinking about
misalignment, because the throughput as measured by Conky was a factor 2
larger than measured by ZFS itself (zpool iostat). The disk read-out is
Disk /dev/sdd: 1.82 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: 007-1R8174
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: F4581F88-2B2E-4C16-8D73-E55EC05CF987
Device Start End Sectors Size Type
/dev/sdd1 2048 4095 2048 1M BIOS boot
/dev/sdd2 4096 1054719 1050624 513M EFI System
/dev/sdd3 1054720 5249023 4194304 2G Linux swap
/dev/sdd4 5249024 9443327 4194304 2G Solaris boot
/dev/sdd5 9443328 3907029134 3897585807 1.8T Solaris root
Many partitions start on the 2048 Byte boundary or a multiple thereof,
which means that you have a misalignment and you double the number of IO
Operations needed to read/write ZFS records. The last ROOT partitions
starts at 4k sector number 2305½. In my opinion a serious bug in the ZFS
implementation of Ubuntu, however most people will not have the issue,
because they run mostly from 512 Byte aligned SSDs or nvme-SSDs.
I think it should be a general rule on 4k HDDs and SSHDs you should
align partitions on 4K boundaries.
** Affects: ubiquity (Ubuntu)
Importance: Undecided
Status: New
** Package changed: conky (Ubuntu) => ubiquity (Ubuntu)
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https://bugs.launchpad.net/bugs/1949252
Title:
Ubuntu installed with wrong ZFS partition alignment for 4k HDD
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