Did you know (2) …

November 28, 2013

It’s happened again … the brain stopped working. So instead of writing something new I’m going to tell you about another little quirk of our controllers … just in case you need a bit more technical information. In reality I’m knee deep in the middle of redeveloping all my technical training slides and the brain needs a rest …

Boot order. In the bios of a Series 7 and newer controller these is an option to “Select Boot Device”. Now that sounds pretty simple and surely I can’t be blogging about that for very long? Well there is a bit more to this than meets the eye.

1. You can have multiple arrays on a controller

2. You can have raw devices (pass through) – disks that are shown straight to the OS

3. You can boot from any of the arrays, or any of the raw devices

Hmmm. The age old way of changing the boot order was to go into the raid array configuration utility (card bios) and use control + B to set the boot order. The array on the top of the list is the one that the card will boot from. Unless of course, there is a raw device (uninitialised drive) being presented to the OS … and then, of course, only if that drive has been put in in the boot order.

But wait, you can’t set raw devices using control + B as they don’t appear in the list. That is where the option “Select Boot Device” comes into it’s own. It allows you to choose raw devices (uninitialised disks) from the list and add one to be the boot device. Now what happens to your RAID array if you do that? Simply put the raw disk will precede the RAID array in the boot order.

A little trick here is that since the raw disk has no metadata we can’t store the fact that it’s a boot device on the disk … that information has to be stored in the controller. If that device fails then the boot order will revert to the first array in the list. So we have two ways of setting the boot device because each one is attached to two different types of disks (raw disks and RAID arrays).

Of course, all of this needs to be handled by your motherboard bios … and you need to set the correct device in the motherboard for your system to boot from (but they tend to handle that automatically these days).

I just wouldn’t want you getting confused :-)



Sometimes I surprise even myself …

November 5, 2013

I wrote the following back in early 2009. I’ve never really thought too much about how right or wrong I am … that’s for the critics to work out. However read the following in italics, then read on about our latest incarnation of hybridness (is that a word?)

“… (lots of blah which I’ll save you reading) …

What storage technologies will survive into the future and what won’t?

The simple answer to that question which is an extremely safe bet is … they all will.

Will SSD kill off SAS? Did SAS kill off Fibre? Will SATA kill off SSD due to price? No. None of those things will happen for a few simple reasons. Those reasons don’t happen to have much to do with technology … they are more to do with the people behind the technology.

Fibre will survive. SSD will grow in popularity and eat into the 3.5″ SATA market. SATA will move to the 2.5″ market and increase in size to the point where we have insanely huge drives at ridiculously cheap prices. SAS will remain due to the fact that poeple just loved SCSI and can’t bear to give it up, so they’ll accept SAS as it’s heathen reincarnation and live with that because “it just works”.

All of our current technologies will be with us for the forseeable future in the same way your favourite football team will continue to survive. People follow a technology like they follow a football team. Good, bad, indifferent, financially stuffed, incredibly successful … none of that matters. It works for me so I’ll stick with it.

The answer, of course, is that the future will see a combination of the more successful technologies in some sort of hybrid form. The car manufacturers are doing it now and we are all agreeing. Pure electric cars suck. Pure petrol cars suck (petrol that is). Combine the two and you have a winner for everyone. So it is with storage technology.

Pure SATA is too slow and too unreliable. Pure Fibre and pure SAS are too expensive. Pure SSD is nuts (price and capacity). However … combine those technologies into a hybrid creature that uses the best features of each one and you have a winner. So keep an eye out for products that use a little of everything … balancing your performance, capacity and growth factors while keeping your balance sheet in a colour other than red.

Hybrid technology. That’s what will survive. Keep an eye out at a store near you.”

Now either I was ahead of my time, or I’m even more cynical than I had originally thought. Adaptec has just released maxCache Plus with its soon-to-be-available Series 8 RAID controllers. maxCache plus is a tiering technology – where you define what is your fastest down to slowest storage, and the controller/software intelligently stores important data on your fast storage and your unused or unimportant data on the slow stuff.

So now all those different kinds of storage you have in the one box can be made to work together to give you the storage performance you want without throwing out all of our favourite old technologies.

maxCache Plus – find out more on the Adaptec website.