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HyperSCSI Examined
An anonymous reader writes "Eugenie Larson of byteandswitch.com has published a brief article that reviews the HyperSCSI protocol, which like iSCSI allows for an IP based san. The twist of HyperSCSI is that it's opensource, and runs over raw ethernet, avoiding the overhead of TCP/IP. The article has some comments from early adopters of HyperSCSI, as well as some comments from top vendors in the iSCSI industry."
I like the idea. Ethernet hardware is dirt cheap and fast. What it needs is a cheap IDE bridge board. That would let you put some IDE drives in an external enclosure and plug them into the local LAN.
Mea navis aericumbens anguillis abundat
How about UDP? It's IP based, but doesn't have the overhead of TCP.
For people who wouldn't know this kind of stuff, TCP does much to ensure that every packet arrives as it was sent. This adds overheard, but it's hardly ever seen by any end user because it's pretty universal. UDP has no error checking, so it isn't fit for anything where any particular packet matters. On the plus side, overhead is severely reduced. I imagine UDP is used for streaming audio and video, but I don't know.
tuned for SCSI commands and data transfers. This is the particularly interesting part of the protocol. It assumes you're going to be doing bulk transfers, and lets both ends negotiate windows for performance (as opposed to using a sliding scheme).
As I see it, the real problems:
- SMP "experimentally" supported
- client and server can't coexist on same box
- client model is not decoupled enough from the server (a server going down can mean the client could crash)
It appears the driver software needs some work properly implementing what seems to be a nifty protocol. And they want to port it to Solaris. I think they should get the locking and stability down first.
Fuck Beta. Fuck Dice
BTW, Andre Hedrick is one of the main IDE developers for Linux.
I certainly appreciate his IDE efforts, but of course he is going to criticise the technology - his company is an iSCSI company!
What, do they think he is going to say, "Gee, and all this time, I've thinking that iSCSI is the right thing to work on. I'm going to abandon iSCSI right now, and start playing with this HyperSCSI thing."
The Internet's nature is peer to peer - 20050301_cs_profs.pdf
How do SANS based on such things as HyperSCSI handle cuoncurrent filesystem accesses by mutiple different machines, since the device at the other end is just acting as a disk, and the host has to maintain filesystem integrity?
Fiber Channel maximum cable length: 10,000 m
Add the appropriate routers and switches and you can easily go 90 km on dark fiber. Add some appropriate routers onto a fast network (T3, ATM, what have you) and you can go 500 km. With fast FC connected storage at each end. Of course, this sort of solution is used by data centers, not home users. But Fiber is the obvious solution to data storage problems. And there is enough mass in the server storage market now that prices are starting to come down. Of course, if you need fast, redundant, capable storage you won't blink at the cost.
In my universe I'm perfectly normal, it's not my fault you don't live in my universe.
That's a good point, and needs a bit more modding up.
...) evolved for the long thin pipes used to connect computers to one another.
It's worth adding, however, that the hyperSCSI folks are trying to make a distinction between wider-area networks (which they call SWANs for Storage WAN) and local single-segment (since they aren't routing) networks, and arguing that iSCSI is right for the former and hyperSCSI, because it's faster/cheaper, for the latter.
This view has parallels in the history of NFS over TCP versus NFS over UDP, because NFS/UDP is still hanging on in one niche: short-haul, high-speed, low-latency, few-hops, negligible-loss environments.
It also has parallels with the bad old days when direct-attached storage interconnects were much faster than LANs, so one set of protocols (FCP, SCSI, ESDI, IDE, SIMD...)evolved on the short fat pipes used to connect computers to peripherals, and a completely different set of protocols (ethernet, TCP/IP, SDLP,
Similarly, hyperSCSI is an argument that the two domains are different enough to justify different protocols. That seems to be arguing against a historical trend tht says that the short/fat and long/thin differences are vanishing; compare gigE and fibrechannel as _wires_ today.
All of this just reinforces Bourne's general point about ignoring the history. It's pretty clear that NFS over TCP is where the world is going, and the only reason that there's an NFS over UDP hanging around is that's how all NFS used to be, so some still is. When we compare hyperSCSI to iSCSI over TCP, I can't find any reason not to just deploy iSCSI everywhere and be done with it.
iSCSI has drivers for every OS you can imagine, written by CISCO, IBM, Microsoft, and released under the GPL. This is from the iscsi sourceforge page.
This implies for instance that one could boot ones diskless workstation from a collocated netapp on another continent, protected by a an IPsec tunnel. While i could do something similar with ethernet layer tunneled over IP, it leads to many complications and difficult debugging. I have personal experiance with this, as this how our company runs its ethernet layer phone system.
Because the IP checksum and TCP checksum occasionally disagree about the packets' validity in real-world routers and operating systems - they are both needed to provide redundancy and robustness. Stevens' TCP/IP Illustrated cites [Mogul 1992] providing counts of checksum errors on a busy NFS server:
Layer Total packets # chksum errs
Ethernet 170,000,000 446
IP 170,000,000 14
UDP 140,000,000 5
TCP 30,000,000 350
Basically, when absolute accuracy is required the more error checking the better.
The GPL is not specific to Linux. You can have an application built upon Win32 and released under the GPL, and it will not run on Linux. The point of the GPL is not to help any particular operating system, yet to assist software to have a conditional freedom and authority backed by copyright law in recognition that if it were true public domain then it could be "hi-jacked" into another software.
The GPL establishes penalties for people or artificial entities that don't provide the sourcecode of the software, yet the GPL states it is voluntary to accept the GPL and if not accepted then copyright law is the premise for not accepting the GPL's distribution rules. And in copyright law, whoever using the copyrighted software needs the permission of the copyright owner on use of the alleged "software." GPL is a harmless fuzzball, fear the copyright owner.
If you want true freedom, then software would be released anonymously in the Public Domain and the risk is someone could steal the software and claim they own it. An example of a Public Domain work is the Authorized Version Bible aka King James Version Bible of 1611 A.D. All the recent alleged "Bibles" such as "New International Version", "American Standard", "New American Standard", "New King James Version" (false King James AV), and "Century New King James" (false King James AV), and many more are all actualy copyrighted! They are known as false Bibles because in their preface or inserts there is a text from a corporation that establishes conditions of their usage, unlike Public Domain bibles such as the King James Authorized Version Bible and also Gutenberg Bible. Further example, the NIV aka "New International Version" manifests conditions upon the reader: "The NIV text may be quoted and/or reprinted up to and inclusive of one thousand (1,000) verses without express written permission of the publisher, providing the verses quoted do not ammount to more than 50% of a complete book of the Bible nor do the verses quoted comprise more than 50% of the total work in hich they are quoted." In short, the NIV changes the many books of the Bible in such little ways to change the outlook and image of God's message and issues a copyright'd patent proclaiming they own and say how much you can quote without express permition! How long before a alleged "Bible" is released that says you can only read it on Sunday and only upon the permission and interpretation of an alleged "father of the Catholic Church" and you must accept the Catholic Church without condition as the divine authority of all scripture:
"For the Roman pontiff (pope), by reason of his office as VICAR OF CHRIST, and as pastor of the entire Church has full, supreme, and universal POWER over the whole Church, a power which he can always exercise UNHINDERED."
--CATECHISM OF THE CATHOLIC CHURCH, 1994, P. 254 #882
"[W]e hold upon this earth the place of God Almighty."
--POPE LEO XIII
"...We declare, state and define that it is absolutely necessary for the salvation of all human beings that they submit to the Roman Pontiff [pope]."
--POPE BONIFACE VIII, BULL UNUN SANCTUM, 1302
"No person shall preach without the permission of his Superior. All preachers shall explain the Gospel according to the Fathers. They shall not explain futurity or the times of Antichrist!"
--Pope Leo X, 1516
Although I may seem offtopic, my point I try to emphasize is copyrights are evil to the extent they can regulate and infringe upon others by use of truth and law that is vested in the mere essence of man if not written on paper. The GPL uses copyrights for the good of mankind, as if to turn copyrights into a double-edged sword, yet even the GPL can be used for evi
Secured Party, Without Prejudice, UCC 1-207: Creditor
How does ZX meet DR (disaster recovery) requirements of 300 miles?
How does FC operate in mixed vendors (Brocade w/ McData) ?
SAN infected by virus, IPSEC mean anything to you?
Data integrity checksum of the payload?
First question ZX just does not get the job done.
Second question, degraded mode and the customer is not told about the issues. They are generally are left uneducated about the issues/concerns.
Will not explain the obvious in the third.
Read the SPEC for iSCSI RFC for #4.
Regards,
Andre
PS forgot/to lazy to login here