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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: iSCSI virtualization proposalYaron, Jim has a valid point that this is not iSCSI focused. I see this as a Third Party Virtualization, of which a number of companies have such products out today. They also have special host code to support this, as you will need here. But more to the point, it is not iSCSI specific and therefore should be pursued with T10. If that Standard is established, then and then only, we should consider it as part of iSCSI. Lets keep this out of our discussion on Gateways, Proxies, etc. it does not fit there. . . . John L. Hufferd Senior Technical Staff Member (STSM) IBM/SSG San Jose Ca (408) 256-0403, Tie: 276-0403 Internet address: hufferd@us.ibm.com Jim Hafner/Almaden/IBM@IBMUS@ece.cmu.edu on 10/12/2000 10:35:47 AM Sent by: owner-ips@ece.cmu.edu To: Yaron Klein <klein@eng.tau.ac.il> cc: ips@ece.cmu.edu Subject: Re: iSCSI virtualization proposal Yaron, Is this something specific to iSCSI or more general (e.g., applicable to SVP or FCP or even parallel)? If so, I would suggest that this is an issue for T10. Additionally, this can be interpreted in some sense as the initiator being a copy manager and receives (as a target) from the manager (now an initiator) an EXTENDED COPY command in which the destination of the data is the initiator. This point of view changes the sematics a bit (and doesn't quite fit the suggestion from Charles to pass status back through the manager). Do we get the same net function this way? Is there anything that iSCSI needs to do? Can it all be accomplished with implementations within the existing spec? I honestly don't know the answer to these questions (as I haven't really thought about this that hard). Jim Hafner Yaron Klein <klein@eng.tau.ac.il>@ece.cmu.edu on 10-12-2000 02:54:12 AM Sent by: owner-ips@ece.cmu.edu To: ips@ece.cmu.edu cc: Subject: iSCSI virtualization proposal Proposal for iSCSI virtualization: The problem: In order to implement iSCSI virtualization in a local network, we need the following topology: ----------- | | host | | ----------- --------------------------------------------------------- | | | | | | | | | ---------- ---------- ---------- ---------- | | | | | | | | Manager| | Disk A | | Disk B | | Disk C | | | | | | | | ---------- ---------- ---------- ---------- When the host is an iSCSI initiator, the disks are iSCSI targets and the manager is with iSCSI target port to the host and iSCSI initiator port to the disks. The host considers the manager as a "flat" disk space with iSCSI port and is unaware of the disks. The manager manages the disks in some algorithm to construct a combined virtual volume. Consider the following example: Each disk contains 1000 blocks. The virtual volume is thus 3000 blocks. The hosts sends an iSCSI command to the manager to read 40 blocks from address 500. The physical addresses are: A ? 400:409, B ? 300:319 and C ? 600:609. In the current iSCSI protocol, the traffic scenario is: Host -> manager: iSCSI command, read from 500 size 40. Manager -> A: iSCSI command, read from 400 size 10. A -> manager: iSCSI data. A -> manager: iSCSI status. Manager -> host: iSCSI data. Manager -> B: iSCSI command, read from 300 size 20. B -> manager: iSCSI data. B -> manager: iSCSI status. Manager -> host: iSCSI data. Manager -> C: iSCSI command, read from 600 size 10. C -> manager: iSCSI data. C -> manager: iSCSI status. Manager -> host: iSCSI data. Manager -> host: iSCSI status. Problem 1: Traffic on the line is double! Each data packet is transferred twice (from disk to manager and from manager to host). Problem 2: The manager is a bottleneck. Both data and commands of all the system (assuming many hosts and disks) is transferred via it. Solution: Lets add in the iSCSI status message, in the "iSCSI status" field, the following option: 2 - iSCSI reflection Which means that the status contains add-ons of iSCSI command that the host should implement. These commands will implement the original request. In our example it will look as: Host -> manager: iSCSI command, read from 500 size 40. Manager -> host: iSCSI status (with reflection), iSCSI commands (for A, B and C) host -> A: iSCSI command, read from 400 size 10. A -> host: iSCSI data. A -> host: iSCSI status. host -> B: iSCSI command, read from 300 size 20. B -> host: iSCSI data. B -> host: iSCSI status. host -> C: iSCSI command, read from 600 size 10. C -> host: iSCSI data. C -> host: iSCSI status. Benefits: * Data traffic on the line is single. * No bottleneck on the manager. Note: The manager is a software pack. It can be an independent unit, in the host or in one of the disk. It is just schematically stated as independent unit. In conclusion, the addition of the reflection feature in the protocol is minor change, can be optional and will enable the enormous potential of virtualization. Comments are more than welcome, Yaron Klein SANRAD klein@sanrad.com
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