Discussing all things virtualization and storage in the data center.

SATA Patter

OK, so the above title only works if you pronounce SATA as “sata” and not as “sata”  - may be that would work better with sound Wink

It seems that SATA is causing quite a stir in the storage world.  I recently read a post on a forum written by a fellow storage pro with a client who wanted their tier 1 storage on SATA disk – presumably due to the good cost per gigabyte.  The reaction to his customer was the same as what mine would previously have been - to protest and try to persuade his customer away from this heresy.

After reading the post I started to think that this kind of thing is going to become more and more common.  After all, the people who hold the purse strings in many organisations inevitably prefer the cheapest option when it comes to spending money on IT.  Then a second thought came to mind - why do we automatically react with horror at the thought of using SATA disk as tier 1 storage?  Have we been conditioned by the industry to react this way?

Of course I know that certain applications and situations require the higher performing and more reliable FC disks, however, Im starting to think that SATA could be a viable option for more than just archiving.  Now bear with me while I explain why I think this -  

A short while ago while I was contracting for a company in an outsourced environment who needed to add more capacity to one of their customers storage subsystems.  As I was assessing the requirements and putting together my recommendations I came across a slight catch 22 situation –

•    On the one hand the company had a standard where they only put 73GB 15K spindles into this subsystem.

•    On the other hand they were running out of free disk slots in their existing frames and would require an additional frame installing to meet their capacity needs with 73GB spindles.  However, they also had serious space, heat and power consumption problems in the primary data centre which meant they could not install a new frame for quite some time.  This was not an option – the customer needed the additional capacity “yesterday” - isn’t that always the case!

Anyway I looked at the performance stats for the currently installed disks/array groups and found that all of them, as well as the front end channel ports and cache, were sitting around doing almost nothing other than consume electricity heat the room.  So my natural reaction was to recommend the larger 146GB 10K spindles so that we could install twice as much capacity in the limited amount of physical slots available and not have to worry about performance, and all at a cheaper cost. This wasn’t a problem to get management buy-in.  However, because the cache was coping so well - the backend disks were not even a factor - I actually started to wonder whether SATA disk in a RAID 6 dual parity configuration would be a realistic option??

As it turned out for a couple of technical reasons this wasn’t a serious option in this environment.  But it was enough to make me to start thinking that may be we shouldn’t be dismissing SATA disk so quickly.

MAKING THE CASE –

So what really is the “crack” with SATA disks?  Are they as bad as we (or may be its just me) think?

While I do hear that SATA disks are not built with the same quality materials or to as high a standard as FC disks, I am certain that they are not manufactured with the intention to fail quickly.  I must point out that I can’t comment authoritatively on the disk manufacturing process as Ive never actually seen it, but anybody reading this who owns a disk manufacturing plant is more than welcome to invite the bloggers of rupturemonkey.com to come and view the process.  I think its safe to assume a relatively high build quality for SATA disks designed to be installed in enterprise storage arrays.  Disk manufacturers reputations are on the line here!

I also think that we are often quick to associate SATA disks with cheap commodity desktop computers and forget that we are installing them in high end storage subsystems that are designed to be as disk drive friendly as possible with built in mechanisms designed to extend the life of a disk.  They also won’t be turned on and off all the time, which can cause wear and tear on disk drives.  Then of course they are often installed in specially designed “clean rooms”.  All a far cry from the computer that sits on the company receptionists desk, or your laptop, that gathers dust, gets bumped around and suffers the occasional coffee spill.

Of course SATA is not a replacement for FC disks, but I’ve seen many installations where FC disks are overkill.  There seems to be an ethos that because a subsystem is expensive the disks installed must by default have to be top of the range.  Not always true!  Often true, but not always.

Mackem

Lets also not forget the imminent arrival of a replacement for traditional RAID from a new startup company formed by the bloggers of rupturedmonkey.com  This new technology will reduce the overhead caused by parity and double parity calculations on writes, as well as speed up and smooth out the procedure for recovering from failed disks.  See previous post titled “RAID – Time for a better way

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