In the Beginning, There Was SCSI…
Any discussion of modern storage protocols, must begin with SCSI. From its humble beginnings in the 1980s, SCSI is nearly ubiquitous as the underlying technology used by most major storage protocols today. SCSI is an official standard architecture and is overseen by the T10 committee of the InterNational Committee for Information Technology Standards.
SCSI is both a physical cabling specification and a command set. For the purposes of this discussion, I will only be referring to SCSI’s logical definition. It’s been a long time since I’ve worried about SCSI cable lengths, wide, ultra-wide, HVD, LVD, etc. and I don’t plan to start now. Those days are gone.
The SCSI command protocol lives on however. At it’s core, SCSI is a client-server protocol with some special terminology. Here are some common SCSI concepts that are useful to know:
- Initiator - The device which sends (initiates) the SCSI command. This is usually a disk adapter card in the computer system.
- Target - The device which receives and processes the SCSI command. This is generally a storage device (i.e. disk or tape).
- Bus - A physical or logical connection between a collection of initiators and targets. A bus typically contains a single initiator and many targets, but multi-initiator buses are allowed.
- Logical Unit (LU) - The logical representation of a storage device. A logical unit may be a single SCSI hard drive, or as is common in large storage arrays, a logical unit may be a subdivision of the larger array. (It’s possible for a large storage array to contain hundreds of logical units.)
- Logical Unit Number (LUN) -A numerical given to an individual logical unit that uniquely identifies it on a given bus. The term ‘LUN’ is commonly used to refer to the logical unit itself, but this usage is technically incorrect. LUNs are used to identify the source and destination for SCSI commands.
I’m not going to cover the specifics of the commands. For that, please visit the T10 site or Wikipedia. My intent for this installment was to provide these basic definitions and plant the idea that SCSI is the foundation for many of the protocols that we’ll be discussing in future installments.
Related Entries:
IDC Issues Top 10 Storage Predictions for 2008
IDC has published its top 10 storage predictions for 2008. Here’s my take.
1. Storage services models for data backup, archiving and replication will be more appealing to businesses.
I agree completely. More and more companies, especially smaller ones, are realizing that it doesn’t make sense for them to constantly be building ever larger storage infrastructures. The concept of a “storage utility” has been bouncing around since at least 2001, but it has only recently started to take off. Services like Amazon’s S3 and the oft-rumored G-drive are only the beginning.
2. New role-based storage systems will demand tighter integration between the storage layer and content-generating applications.
This one also makes sense. In a business context, storage isn’t important. It’s the data contained within the storage that is valuable. Unfortunately, our ability to categorize and contextualize data has not kept up with our ability to generate it. One of the on-going challenges of data management is to separate the valuable data from the background noise. Making the storage layer more aware of the contents of the data is a logical step.
3. Vendors will build object-based storage systems to classify data and add policies closer to the point of creation.
This is an extension of the above. Today many companies faced with data retention regulations adopt a “keep everything” policy. This leads to multiple challenges beyond the obvious cost of storage. By having a mechanism to automatically classify data as it is created, policy can be enforced in an autonomic manner. For example, the storage system will know that my quarter-end financial spreadsheet needs to be kept for some period of time, while my email asking my coworkers where they want to go to lunch can be discarded immediately.
4. Falling prices of solid-state disk drives will push mainstream adoption.
I’m not as optimistic on this point. I think that a lot more solid state storage will be sold in 2008, but I don’t think that 2008 will be known as the year of the solid state drive. I look for it in laptops and blade servers in 2008. The price point is just going to be too high for use in enterprise storage. Perhaps 2009.
5. Virtual servers will become an ideal conduit for iSCSI.
iSCSI has been predicted to take over the storage networking world since 2004. Every year it gets a little better and gains a little more market penetration, but fibre channel still prevails.
Don’t get me wrong, I like iSCSI. I also think that it is a natural fit with the virtual server ecosystem. The challenge is going to be one of speed. 4Gbit fibre channel is common and 8Gbit is just around the corner. Gigabit ethernet is common, but 10Gbit ethernet is still a bit unusual. Once you start stacking a lot of virtual server images onto your hardware, you’re going to start needing that extra bandwidth. I predict that iSCSI will ultimately be king in the smaller shops, but fibre channel will continue to reign in the enterprise.
6. Value-added storage services will become nontethered from storage infrastructure.
I hope this one comes true. I’m tired of vendors deliberately ignoring open storage standards in an effort to protect their install base. Aperi is a step in the right direction.
7. Full-disk encryption will be prevalent in the data center to satisfy compliance and safe harbor provision rules.
This one is a no-brainer. 2007 was the year of tape encryption. 2008 will absolutely be the year for full-disk encryption. The interesting challenge will be managing the encryption keys. That is ultimately much more difficult than scrambling the bits on the disks.
8. Offerings designed for small and midsize businesses featuring integrated storage and server technology will flood the storage market.
This is already happening.
9. Green storage initiatives will cause companies to seek nondisruptive/partial hardware upgrades.
I’m going to be honest. I don’t get this one. Can anyone help clue me in?
10. De-duplication, thin provisioning and virtual tape libraries will be in demand because of power saving efforts in the data center.
Ah, the buzzword trifecta of de-duplication, thin provisioning, and virtual tape. While legitimate arguments can be made for the power savings generated by storing less data, I don’t agree that virtual tape fits here. Think about it. What consumes more electricity, a virtual tape spinning around on a continuously rotating disk or a tape cartridge sitting quietly in a library? Tape isn’t dead. If anything, tape will become more important as an integral part of the green datacenter.
So, that’s my take on IDC’s 2008 storage predictions. Feel free to post your own comments or predictions. I’ll look forward to revisiting this post next December.
(via Computerworld)
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