Thanks for reply. After performing an additional testing with SSD. I have
more questions.

Firstly, about the additional testing with SSD:
I tested it with SSD (in Linux software raid level 10 setup). The result
shown using dm-integrity is faster than using XFS directly. For using
dm-integrity, fio shows lots of I/O merges by the scheduler. Please find
the attachment for the result.

Finally, please find the questions below:
1) So after the dm-integrity journal is written to the actual back end
storage (hard drive), then fsync would then report completed?

2) To my understanding, for using dm-integrity with journal mode. Data has
to written into the storage device twice (one part is the dm-integrity
journal, the other one is the actual data). For the fio test, the data
should be random and sustained for 60 seconds. But using dm-integrity with
journal mode is still faster.

Thanks,
Patrick

On Sat, Jan 4, 2020 at 1:14 AM Mikulas Patocka <mpatocka@redhat.com> wrote:

>
>
> On Fri, 3 Jan 2020, Patrick Dung wrote:
>
> > Hello,
> >
> > A quick question on dm-integrity. Does dm-integrity layer honors fsync?
>
> Yes it does.
>
> However, it writes data into the journal and when the journal is flushed,
> it reports the fsync function as finished.
>
> On a mechanical disk, writes to contiguous space (i.e. the journal) are
> faster than random writes all over the disk, that's why you see better
> performance with dm-integrity than without it.
>
> Mikulas
>
> > I was testing dm-integrity and performance. It had a strange result that
> using dm-integrity with journal is faster than a normal file system or
> dm-integrity with
> > bitmap (no journal). fio is used for testing the storage performance.
> The device is a SATA hard disk drive. Then I created a 100GB partition for
> testing.
> >
> > Below is the test cases:
> >
> > 1) XFS on a partition directly test case
> >
> > 2) dm-integrity: crc32c on a partition with default setting journal
> commit interval is 10 seconds. Then create XFS on it. test case
> >
> > 3) dm-integrity: crc32c on a partition default setting journal commit
> interval set to 5 seconds. Then create XFS on it.
> >
> > 4) dm-integrity:  crc32c on a partition default setting but using bitmap
> instead of journal. Then create XFS on it.
> >
> > FIO command:
> >
> > fio --filename=./t1 --direct=1 --rw=randrw --refill_buffers
> --norandommap --randrepeat=0 --ioengine=sync --bs=4k --rwmixread=75
> --iodepth=16 --numjobs=8 --runtime=60
> > --group_reporting --fsync=1 --name=4ktest --size=4G
> >
> > Result:
> >
> >  1. Read/Write IOPS: 117/41. Read/Write Speed 481KB/s 168KB/s
> >  2. Read/Write IOPS: 178/59. Read/Write Speed 732KB/s 244KB/s
> >  3. Read/Write IOPS: 169/57. Read/Write Speed 695KB/s 236KB/s
> >  4. Read/Write IOPS: 97/32. Read/Write Speed 400K/s 131KB/s
> > The original discussion in:
> https://gitlab.com/cryptsetup/cryptsetup/issues/513 . Milan Broz said the
> dm-devel mailing list is a suitable place to discuss the probem.
> >
> > Thanks in advance.
> >
> > Patrick
> >
> >