Discussion on:

Storage array capacity: Performance vs. cost

Very informative post, but I'm curious about the performance multipliers for RAID. Based on this and your previous article, reading is always 1-to-1 regardless of RAID configuration. I would think that in a configuration where data is mirrored we would gain some read performance (i.e. a multiplier like 0.8 or such) since the RAID can be reading the blocks from multiple drives simultaneously.

You raise a good point. Improved read performance (that 0.8 factor, for example) would have the effect of reducing the total IOPS need, particularly for large read workloads. For large write workloads (say, the 70% examples), the read benefit would be mostly negligible, but still there.

I'll have to kick that one around a bit!

Scott

The read benefit is accounted for in the calculation since it uses the total IOPS based on all of the spindles in the config.

The SSDs are really expensive on the surface, and I haven't been able to justify purchasing them but there are some cases where they might work out. Obviously people are buying them, just not me! If you have an application that is slow on a midrange system, where hundreds of users are waiting to do their jobs, or transaction are being slowed down and effecting the business, you should be able to get buy-in for such a purchase. It's probably going to be cheaper to purchase a few SSD than to go out and get a V-Max or USPs. Also if you have limited space in the datacenter, or power concerns, or HVAC limitations, SSDs might work out to be better in the long run.

Curious why the price of the EMC 1TB Sata disk is so high, considering you could have three WD RE3 disks for the same cost. Surely the increased spindle count could be made to outperform EMC in either reliability or speed, if not both.

i.e. For every single EMC SATA disk, for the same or similar cost you could have two mirrored WD Raid Edition disks plus a cold or hot spare. Does a single EMC disk beat that?

when can we expect the slash rates of SSD...???