Promise announced that they’ll now be offering 1TB drives in their Vtrak RAIDs. While it’s great to have the additional space, the darn things are just a tiny bit faster too. If bigger drives means faster, why? Doesn’t it seem like bigger drives, and thus more storage density, would make for slower speeds, not faster…
Well, storage density is a measure of the number of bits that can be stored on a track, area of surface, or in a given volume. Areal density is the amount of data that can be placed onto a piece of storage, generally measured in bits per square inch. Higher density is typically better as it gives you more data to store in a limited amount of physical space. With all things computer related, density typically has a direct relationship with capacity obviously, but also with performance and of course price.
Increasing storage density improves transfer speeds because the same amount of data takes up less space on the surface of larger disks, given the fact that the data is packed in there so much more tightly. Given the small amount of surface space that a drive head needs to access, there is less movement of the head, arguably one of the slower components of the drive and therefore higher density means more data per movement of the drive head. And of course, less movement of anything in a computer means less power is being used, which makes the power bills go down noticeably if you’ve got a whole lot of hard drives.
So if you can improve the performance for one drive slightly then the performance is compounded a little more over an entire RAID, where you are writing data to a number of drives to increase performance. In most SAN environments you have multiple RAIDs where you are round robining data. This makes a small performance increase for one drive compound greatly to hundreds of drives provided that the medium with which your hosts are communicating with the SAN can handle the speed.
To wrap all of this up, if you can upgrade your drives, it can’t hurt, but won’t just increase your available capacity by 30%, it will theoretically also increase your speed, although only benchmarking the new drive modules will tell a good compelling story about how much it will do so, or whether the fibre channel has already been saturated and it won’t show much of a difference.
