[OpenIndiana-discuss] Slow write speeds on HGST HUH728080AL5200 via COMSTAR target

[Stephan Budach]

Hi,

----- Ursprüngliche Mail -----
> Von: "Stephan Budach" <stephan.budach at jvm.de>
> An: "Discussion list for OpenIndiana" <openindiana-discuss at openindiana.org>
> Gesendet: Sonntag, 2. Juli 2017 10:09:37
> Betreff: [OpenIndiana-discuss] Slow write speeds on HGST HUH728080AL5200 via	COMSTAR target
> 
> 
> Hi eveyone,
> 
> 
> I have setup three Supermicro storage servers, which are running HGST
> HUH728080AL5200. I wanted to export each drive as a raw LUN over
> iSCSI. A fter having installed the latest OI hipster and recovering
> the primary label from the backups on each disk (which were all
> bad/corrup, for whatever reason), I went forth and used fdisk to
> partition the drives to one big partition, on which I created a LUN,
> which I then exprted over iSCSI.
> 
> 
> The issue I am now facing is, that the read speeds are very good, but
> writing is really slow. The drives are HGST HUH728080AL5200 and HGST
> states the following about them:
> 
> 
> 
> 
> Interface: SAS 12Gb/s
> Capacity: (GB) 8TB
> 
> Sector Size (Variable, Bytes/sector): 4Kn: 4096, 4112, 4160, 4224
> 
> 
> Could it be that the fact that the COMSTAR LUN only advertises 512
> byte sectors leads to this issue and if yes, can I do something
> about that?
> 

So, it turned out, that my suspicion about COMSTAR target only being able to export devices advertising a 512-byte block size. The afore mentioned HUH drives are native 4k, but the LUNs on the target server - in this case this is a S11 box, created a zpool with ashift.9 vdevs.

To veryfy that I tweaked the sd.conf on one of my new OI boxes to map all COMSTAR LUNs to have native 4k block sizes. That did the trick on OI. Interestingly, the zpool that I created on my OI box using -o version=28 imported just fine on S11 and since the vdevs were ashift-12 and the performance on S11 became very reasonable.

Does anyone happen to know, if it's possible to trick S11 into regarding COMSTAR LUNs as being 4k drives, or is the detour via OI the only way to create a zpool with raw iSCSI LUNs against native 4k COMSTAR target drives?

Cheers,
Stephan