From: Ross S. W. W. <RW...@me...> - 2011-05-27 21:17:04
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On May 27, 2011, at 5:02 PM, "George Shuklin" <geo...@gm...> wrote: > > On 27.05.2011 23:10, Ross S. W. Walker wrote: > > Lars Ellenberg [mailto:lar...@li...] wrote: > >> Also, since the targets don't know of each other, they would happily > >> give out concurrent reservations each. > > Let me expand on how bad this is by saying if this volume were a MSCS > > or a VMware VMFS or a GFS or a OCFS volume it would be quickly > > corrupted beyond repair. > > > > Also, you can have double, triple, quad the throughput on a single > > head, with double, tripe or quad NICs each on a separate subnet, > > and the initiator making a separate session on each subnet and > > multipathing set to round-robin. > > > Thank you. > > But, still, can you show examples when this configuration will damage > data? I actually expects that iscsi simply acts like 'read, write' layer > over block device and (with blockio) is like a simple stateless proxy to > disk, Which kind of activity is 'statefull' for iscsi? > ISCSI with IET isn't stateless by any means. IET actually does full emulation of the SCSI layer, translating READ/WRITE into OS read/write operations, performing task management and reservation management. An example of a configuration that will cause damage that is readily understandable is any cluster file system that uses SCSI reservations to control which host can write to a shared file system. If two hosts both connect to two separate iSCSI targets then both may think they have exclusive access to the file system, both flush their buffers at once and you end up with a collision that will corrupt the file system. -Ross ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof. |