[OpenIndiana-discuss] [zfs] zfs + iscsi = poor sequential reding performance

[Tomasz Kloczko]

> I used to use  ZFS volume for local VirtualBox use and I know that moving
from 4K block volumes to 64 or 128K improved their speed largely and also
with sync=disabled

BTW sync=disabled .. it improves write IOs only (reduces avg latency as
sync() are ignored) and should be not generally used as when system will
crash it may cause data looses. As well sync=disabled is causing snapshots
inconsistency.
sync=disabled is generally more for temporary usage to for example reduce
importing time of some data (for example importing text dump to SQL engine).
In all other cases main technique used on improve write speed should be (as
long as it is only possible) using ZIL.
I understand that this may be a bit problematic on use iSCSI as usually
number of necessary ZIL vdes may vary in time :)

And back to sequential reads ..
Probably to improve read IOs and especially sequential reads better would
be possible by tune ZFS read ahead settings.
In kstat zfs::arcstat metrics are few helping tune those settings and check
how effective current RA settings are (misses/hits ratio to RA data).

kloczek

Tomasz Kłoczko | Tel: 0774 1209067 | LinkedIn: *http://lnkd.in/FXPWxH
<http://lnkd.in/FXPWxH>*

On 26 April 2016 at 00:06, Nikola M <minikola at gmail.com> wrote:

> On 04/23/16 02:26 PM, Сисадмин wrote:
>
>> for christ sake
>>
> This list is about Openindiana/illumos support so even I have some
> sympathies for proprietary VMWare/Windows users, there is just too many
> things in between that leaves many possible issues open in the chain of
> your use case and test scenario.
> You can use kvm , solaris zones, VirtualBox and kvm and VBox inside zones
> on Openindiana/illumos. (and dilos has Xen on illumos)
>
> Your conclusion about zfs+iscsi is most probably generally wrong and
> unsuited, looking at your config.
> (*and I ask you not to put conclusions in the topic in the first place
> that might hurt OI and zfs)
> I can suggest several things and I suggest that you use
> Openindiana/illumos on hardware and installed as an OS on machine:
>
> First, I recently had some issues with 2 directly cable-connected OI
> machines (much lower spec) with speed not being as expected - try using
> some switch in between?
> Secondly, I think that you should NOT mix hard disk types in the
> pool(512k/4K) - ashift= should be the same across the pool.
> Also, you got to give your zvol volblocksize parameter bigger values then
> 4K, at least 64K and re-run, also blocksize that suits your use case might
> not be best for other use cases, so you might test what blocksize you
> mostly want and for what zvol/iscsi use. (avery zvol can have different
> blocksize, same goes for datasets with files).
> And finally, try to experiment with sync=disabled for your zvols and see
> how that helps them behaving faster.
>
> I used to use  ZFS volume for local VirtualBox use and I know that moving
> from 4K block volumes to 64 or 128K improved their speed largely and also
> with sync=disabled
> and that actually, by using zvols exported via ISCSI IMPROVES disk speed
> for my VMs, then using them as just block devices serving as disk for
> VirtualBox VMs.
>
> You are free to join on #openindiana and #illumos on Freenode etc.
>
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