Folks, I'm working on a setup where I connect to several iSCSI targets, then setup raid-5 on those iSCSI target volumes (The iSCSI targets are themselves raid devices, we are adding a raid-5 layer here to cover the case of a controller/target failure). We use this very large raid5-of-iscsi-targets as an LVM volume group so that we can carve out logical volumes that safely span across multiple iscsi targets. We then present these LVM volumes as iSCSI targets using IET.
In general, this seems to work OK, but when shoving large writes to the constructed iscsi target we see very bursty writes. It will write quickly for about 30 seconds, then falter to almost nothing for 20 seconds, then resume quick operations, and repeat. This is visible both from the fact that during the 20 seconds of slow the filesystem is unresponsive, and also that the network use goes drastically lower during that time. I'm wondering a couple of things: 1) Is there any known problem with passing through two layers of iscsi? 2) Is this type of bursty traffic normal? 3) This may be related to the queue_depth filling up - is there an easy way to see the depth of the queue in real time? (Not the setting, but the actual state of the queue) I know the setup is a bit convoluted, so here another view of it. The physical data blocks are on the left, becoming more layered to the right until we hit our "production" servers. (This is all pre-production now) SATA_disks -> Raid6_controller -> IET(blockio) -> (next box) -> open-iscsi -> md_raid5 -> lvm -> Logical_volume -> IET(blockio) -> (next box) -> open-iscsi -> filesystem_on_production_server It is when writing to that filesystem the problem becomes pronounced. Any insight that anyone has on this would be very welcome. Thanks, -Ty! -- -===========================- Ty! Boyack NREL Unix Network Manager [EMAIL PROTECTED] (970) 491-1186 -===========================- --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to email@example.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/open-iscsi -~----------~----~----~----~------~----~------~--~---