Quoting Stan Hoeppner stan@hardwarefreak.com:
Rick Romero put forth on 1/14/2011 8:29 PM:
And that's assuming a platter squeezing in 1TB of data at
7200RPMs doesn't get a comparable performance improvement to a higher rotational
speed on a lower volume platter...Size and density are irrelevant. Higher density will allow
greater streaming throughput at the same spindle speed, _however_ this does
nothing for seek performance. Streaming performance is meaningless for
transaction servers. IOPS performance is critical for transaction servers. Seek performance equals IOPS performance. The _only_ way to increase mechanical disk IOPS is to increase the spindle speed the or the speed of the head
actuator. If you've watched mechanical drive evolution for the past 20 years you've seen that actuator speed hasn't increased due to the physical properties
of voice coil drive actuators.Hell for the price of a single 250gb SSD drive, you can RAID 10 TEN 7200 RPM 500GB SATAs.
I think your pricing ratio is a bit off but we'll go with it. You'd get 50,000 4KB random IOPS from the SSD and only 750 IOPS from the RAID 10. The SSD could handle 67 times as many emails per second for 10 times the cost. Not a bad trade.
So while, yes, my 10 drive SATA RAID 10 ONLY performs 166MB/sec with a 'simplistic' dd test, In reality I just don't think Joe User is going to notice the difference between that and the superior performance of a single SSD drive when he POPs his 10 3k emails.
But Joe User _will_ notice a difference if this server with the RAID 10 mentioned above is supporting 5000 concurrent users, not just
Joe. Responses will lag. With the SSD you can support 10000 concurrent users
(assuming the rest of the hardware is up to that task and you have enough RAM) and responses for all of them will be nearly instantaneous. This is the difference SSD makes, and why it's worth the cost in many situations. However, doing so will require an email retention policy that doesn't allow unlimited storage--unless you can afford than much SSD capacity.You can get 240,000 4k random IOPS and 1.9TB of capacity from two of these in a software RAID0 for $6,400 USD: http://www.newegg.com/Product/Product.aspx?Item=N82E16820227665
That's enough transactional IOPS throughput to support well over 50,000 concurrent IMAP users, probably far more. Of course this would require a server likely on the order of at least a single socket G34 AMD 12 core
Magny Cours system w/2GHz cores, 128GB of RAM, and two free PCIe X4/X8 slots
for the SSD cards, based on a board such as this SuperMicro: http://www.newegg.com/Product/Product.aspx?Item=N82E16813182240 (Actually this is the perfect board for running two of these RevoDrive X2 cards)
I use pricewatch - so, yes, we may be talking refurb drives, but this is not an issue when you're saving enough money to just buy a few more of items you're already buying.
Also, if your filesystem is using 4k clusters, aren't you only using 1 random IOPS for a 4k email? It just sounds to me like if you plan 'smarter', anyone can avoid the excessive costs of SSD and get 'end user similar' performance with commodity hardware.
Rick