[SunRescue] Info on Sun Multipack and disk arrays in general (long)

[Patrick Giagnocavo]

on 12/2/2000 6:26 AM, Christopher Byrne at chris at chrisbyrne.com wrote:

> All,
> 
> There has been a huge amount of interest in the Sun MultiPack storage array
> I listed here a few days ago. Unfortnately most of that interest was
> somewhat uninformed as to what the MultiPack is, what it does, and how much
> it is worth. 

Chris, I hope you don't mind with me jumping in on a few points.

> There are four basic types of external storage. The simplest and least
> expensive is an external drive housing. This basically acts as a connector
> and power supply for a drive inserted into your SCSI chain. There are no
> benefits assoicated with this except the ability to add storage without
> cracking open your case. These systems are almost never hot swappable or hot
> pluggable and provide no redundancy, fault tolerance, or performance
> increase.

True, depending on how you define redundancy.  Multiple drives on a chain,
configured in a RAID configuration, might provide redundancy/fault tolerance
as long as the SCSI controller didn't fail. Of course, running ALL traffic
over one chain is not good for performance reasons, and if the SCSI
controller fails you are SCREWED.

You can buy drive trays at many places (MicroCenter, Fry's) that allow for
hot-plug or hot-swap capability.  You need to be certain that your SCSI
controller knows what to do if you yank a drive though :-) .  Another
disadvantage of these trays is that they usually require a 5.25 inch device
bay, so they take up lots of space in comparison.

> The MultiPack doesn't officially support the new 73 gig drives (big bucks),
> but they do work. Of course finding a 1" high 73 gig drive with an SCA plug
> for less then 2k is pretty much impossible, if you can get one at all. The
> more common 1.6" or 2" high drives are not compatable. If you fully
> populated the box with twelve 73 gig drives you would have an almost 900
> gigabyte array. Throw in the slots in your Sun box itself and add volume
> management software, and you can build a more than 1 terabyte storage array
> in two small boxes for less than 30 grand. Just to put it into perspective,
> a terabyte is about 333,000 MP3's, 1600 full CD's worth of music, or about
> 200 full screen high quality surround sound movies.

Right, but but NO ONE would spend the money on so much storage and not put
it into some kind of RAID configuration.

If you set up RAID 1 (mirroring) you "spend" one drive for each drive you
use.  In such a case, you divide total storage capacity by 2.  So 900GB
would become 450GB.

With good SCSI controllers or RAID software, you can almost double your read
performance because (since the data is mirrored and is the same on each
drive) you can choose which drive to read from - so you could have two
drives reading different data.  Write performance is basically the same as a
single drive.

RAID 5 - divide by 1.25 - 900GB becomes 720GB.

Cordially

Patrick Giagnocavo