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Writing speed on FreeBSD 13.1-p2 amd64 with ZFS

This is a repeat of the test I ran in 2020 on the same desktop hardware, but now using the ZFS filesystem. Additionally, I’m now also testing the harddisk in the desktop.

Again, the test is writing approximately 10 GB data from /dev/zero to a file using dd.

The big difference between now and two years ago is that both the SSD and the HDD are using the ZFS filesystem instead of UFS.

Most of the SSD (except for swap) is part of the zpool pool. The zstorage pool occupies the HDD.

The zroot pool contains the root filesystem, and basically everything except /home, which is on the zstorage pool. In contrast to the pool on the SSD, that on the HDD is on a GELI encrypted partition.


First the write test to the SSD:

> dd if=/dev/zero of=/tmp/foo bs=10M count=1000
1000+0 records in
1000+0 records out
10485760000 bytes transferred in 1.898418 secs (5523418767 bytes/sec)

This is astonishingly fast; 5523 MB/s or 5267 MiB/s. To say that it is significantly faster than UFS would be an understatement.

I’m not sure is this is a meaningful test, but I would not know how to generate such huge amounts of data otherwise.

If I use /dev/random as the source, throughput drops by an order of magnitude. Probably because of the need to generate random data.

By default, the ZFS cache (adaptive reactive cache; “ARC”) uses most of the free memory. On my machine, I’ve limited it to 2 GiB.


According to camcontrol identify ada0:

pass0: <WDC WD4002FYYZ-01B7CB1 01.01M03> ACS-2 ATA SATA 3.x device
pass0: 600.000MB/s transfers (SATA 3.x, UDMA6, PIO 8192bytes)

protocol              ACS-2 ATA SATA 3.x
device model          WDC WD4002FYYZ-01B7CB1
firmware revision     01.01M03
serial number         ********
WWN                   ****************
additional product id
cylinders             16383
heads                 16
sectors/track         63
sector size           logical 512, physical 512, offset 0
LBA supported         268435455 sectors
LBA48 supported       7814037168 sectors
PIO supported         PIO4
DMA supported         WDMA2 UDMA6
media RPM             7200

The test on the HDD:

> dd if=/dev/zero of=/home/rsmith/tmp/foo bs=10M count=1000
1000+0 records in
1000+0 records out
10485760000 bytes transferred in 54.703728 secs (191682730 bytes/sec)

This is 191.7 MB/s or 182.8 MiB/s. Much faster than the last SATA 2 HDD’s that I tested. But significantly below the 600 MB/s claimed by the pass0 device. I suspect the encryption overhead plays a role in that.

Unfortunately I did not run the test with a UFS filesystem; that would have been interesting to see.

For comments, please send me an e-mail.

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