Hi Alexis, I was just taking a look at the issue you opened with Red Hat about this.
It appears to me that the sd driver for all SCSI disks is setting the max_sectors limit for the queue to the optimal transfer length when sanely reported. So the SCSI disk driver is limiting to the optimal length at all times, while the NVMe code is reporting different optimal and maximum limits to the block layer. The SCSI target code is just passing the block layer limits through to the initiator, so when exposing an NVMe namespace as an SCSI disk the smaller optimal transfer length gets used as a maximum limit on the SCSI initiator. I'm going to ask around and see if I can't get a better understanding as to why the sd driver works that way and if optimal transfer length when reported by SCSI disks are expected to be as small as this NVMe device is reporting. I don't think this is an iSCSI specific issue in this case. - Chris On Sun, Nov 21, 2021 at 6:31 PM Alexis Oosterhoff <[email protected]> wrote: > > Hi, > > Looking into whether this is a bug, or an expect behavior with kernel 4.18+ > > RHEL 8.4 on AWS r5.xlarge hardware type, attaching nvme disks, observing the > nvme device is configuring optimal_io_size to 4KB > i.e. > /sys/devices/pci0000:00/0000:00:1c.0/nvme/nvme4/nvme4n1/queue/optimal_io_size > 4096 > > When attaching this device remotely using Linux-IO, the initiator device is > using the target's 'optimal_io_size' to set the max_sectors_kb. > i.e. > /sys/devices/platform/host1/session8/target1:0:0/1:0:0:0/block/sdb/queue/max_sectors_kb > 4 > > This does not seem to be correct behavior. optimal_io_size and max_sectors_kb > should not be directly related. Do not observe this behavior with RHEL7. > > target: > - RHEL 8.4, 4.18.0-305.12.1.el8_4.x86_64 > initiator: > - RHEL 8.4, 4.18.0-305.12.1.el8_4.x86_64 > - iscsi-initiator-utils-iscsiuio-6.2.1.2-1.gita8fcb37.el8.x86_64 > - iscsi-initiator-utils-6.2.1.2-1.gita8fcb37.el8.x86_64 > > > Thanks, > > Alexis. > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/open-iscsi/1b70c5d5-bb56-4f35-948b-1a2cbde569ban%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/CAPnfmXLkC1tUWMS3cGiynB_-gvLSngsNwPpiyN-brQ14x9X_kg%40mail.gmail.com.
