Re: Network very very slow... was iSCSI and jumbo frames

[BERTRAND Joël <joel.bertrand%systella.fr@localhost>]

Michael van Elst a écrit :
> On Tue, Feb 02, 2021 at 03:55:10PM +0100, BERTRAND Joël wrote:
>> Michael van Elst a écrit :
>>> joel.bertrand%systella.fr@localhost (=?UTF-8?Q?BERTRAND_Jo=c3=abl?=) writes:
>>>
>>>> 	But jumbo frames and Intel adapter don't increase NAS throughput :
>>>>              204Mb           407Mb           611Mb           814Mb
>>>
>>> Where does this information come from?
>>
>> 	iftop.
> 
> But with what kind of disk operation?

	All operations : read, write, by dd or bacula-sd. If I understand,
bacula only writes sequential data files. Filesystem on this iSCSI
volume is ffs (v2) with log (and of course without sync or async options).

> iSCSI naturally has a higher latency than a direct attached disk.
> To utilize a link you may need to generate more requests in parallel.
> 
> For writing that's not that difficult as the client will buffer enough
> data. For reading you need large buffers or significant read-ahead to
> trigger concurrent I/O.
> 
> You may also need to tune TCP/IP on the client.
> 
> You could start a test with reading from the raw iSCSI volume
> with dd. You need a read buffer of at least 1MB to get the
> maximal concurrency.
> 
>> [ ID] Interval           Transfer     Bitrate
>> [  5]   0.00-10.00  sec  1.08 GBytes   931 Mbits/sec
> 
> That looks reasonable for a Gigabit interface.

	Of course, but with dd, I only obtain :

legendre# dd if=/dev/zero of=/opt/bacula/test.dd count=10 bs=10m
10+0 records in
10+0 records out
104857600 bytes transferred in 0.537 secs (195265549 bytes/sec)
legendre# dd if=/dev/zero of=/opt/bacula/test.dd count=10 bs=100m
10+0 records in
10+0 records out
1048576000 bytes transferred in 53.396 secs (19637725 bytes/sec)
legendre# dd if=/dev/zero of=/opt/bacula/test.dd count=10 bs=1000m
10+0 records in
10+0 records out
10485760000 bytes transferred in 1026.927 secs (10210813 bytes/sec)
legendre#

186 MB/s for the first file. 18,7 MB/s for the second one and about 10
MB/s fort the third one.

And I don't understand. If iSCSI target or raid6 subsystem on qNAP were
the bottleneck, CPU load should be greater than 1 and it's not the case.
Maybe I will try to add a SSD disk as cache (but I'm not sure that this
NAS supports cache over USB3).

	Best regards,

	JKB