[Dovecot] SSD drives are really fast running Dovecot

[Rick Romero]

Quoting Stan Hoeppner <stan at 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