NAS performance

[Amadeus1756]

Hi all,

I've been looking at buying a NAS box.
One thing that has always seemed odd to me is the rebuild time required when a disk is replaced, or there is some expansion. It seems that even with the faster models (e.g. Netgear ReadyNas Pro, QNap x59+), it will take many hours to rebuild an array (even if the disks are largely empty).
At work one of my Dell servers (cost about £1500) had 2x1TB drives (about 85% full) configured in RAID1. When one of the disks died and a new one was slotted in, it took about 90 minutes to rebuild the array and that's when the machine is being heavily utilised by about 50+ people.
I'm assuming that my Dell has some hardware acceleration in it, but why is this not prevalent in the more expensive NAS boxes? The difference in times (8+ hours vs 1.5 hours) is tremendous (assuming it's not just a difference between using RAID1 and RAID5).

Any thoughts?

Thanks

 

[ntm1275]

Consumer NAS boxes tend to use software raid, whereas I assume your Dell Server probably was using hardware raid

From what I've read by Googling, it seem to be that software raid is using the CPU to do it's work, when hardware raid has it's own hardware specifically for the task

It appears that it is well known that hardware raid can rebuild an array faster than software raid

 

[Amadeus1756]

That all makes sense and I assumed something similar.
However, the cost of a largish consumer NAS is not far off the cost of my Dell and the Dell has all sorts of other things in it - video card etc. If the Dell machine was 3x the cost, then sure, it could be a price-sensitive issue, but it's not - I just don't see why there are no pro-consumer NAS boxes with hardware RIAD built in.

Rgds

 

[teknojnky]

because hardware costs more.

your server is a server with raid.

consumer nas, are storage appliances with raid, not 'servers'.

nas boxes don't need 'hardware' when they can use the host cpu for free, at the potential cost of longer rebuilds etc.

the apps/addons/plugins that nas boxes can run are secondary to the raid.

where as in a real server, the apps on the server box are primary, and the raid is secondary.

 

[Amadeus1756]

the apps/addons/plugins that nas boxes can run are secondary to the raid.

Indeed - RAID is the primary goal of a NAS box, so one would at least expect it to have an option of hardware RAID, even if that were constrained to the more expensive models.

Rgds

 

[kamina]

Indeed - RAID is the primary goal of a NAS box, so one would at least expect it to have an option of hardware RAID, even if that were constrained to the more expensive models.

Rgds

I guess the line has blurred during the recent years. Dell has also offered dedicated storage devices though they where mainly rebranded EMC devices (and cost quite a bit more).

Appliances tend to cost more, and it's not always the hardware. Look at high end routers, you could do the same (well close) with an x86 server but it just would not be the same.

Nas devices started up as a simple inexpensive way to get a bit of storage when you did not want a big dedicated box or did not have the case for a real SAN device. Performance was bad, but the price was significantly less. Lately these devices have gotten more and more features and the performance has gone up a lot. While a hardware raid card would give far better rebuild speeds you would need quite an expensive card to get the 100MB/s throughput that the current better NAS devices are reaching.

Sure it's a compromise, and if the manufacturers felt they could make a lot of money with a different design they would probably do it.

 

[Amadeus1756]

I guess it needs someone like Apple to come along and make a step-change. We'll look back at what we used before and be amazed!

Rgds

 

[eikka]

I guess it needs someone like Apple to come along and make a step-change. We'll look back at what we used before and be amazed!

Rgds

You mean something like... this? http://www.apple.com/timecapsule/

 

[Amadeus1756]

Mmm, I was thinking of something a little more "industrial"...