Subject hardware: help to choose better disk configuration for FB 2.x server
Author Cristiano
Hi, everyone.

First of all, forgive me by my bad grammar. I'm a brasilian user and will try to do my best with english language.

Second, this post will be a bit long. Please be patient to while I explain the situation.

So, lets go.

I'm running FB 1.5 (linux, classic) and planning the upgrade to 2.5 (linux, superclassic). In my labs I've noticed a great downfall performance in FB 2.1 compared to 1.5. This situation is due to a fixed problem in 2.1, about forced writes malfunction on FB 1.5 (due to a linux kernel bug -

So, I realize that if I want to run FB 2.x with forced writes turned on, and with the same performance from 1.5, I need to upgrade my hardware. And I'm doing it, but I'm stuck with some disk config issues, due to improve performance.

The main doubt is about wich type of disk is better: HDD or SSD (solid state disk).

Have anyone ever tested FB (2.1 ou 2.5) with forced writes turned on under a SSD?

If yes, is there some increase in the performance, relativo to HDD? Can you tell me about the read and write performance, compared with HDD?

I'm buying a Dell PE 410 to serve the FB. This box have a dual Xeon X5670 (six core; 12 Mb cache L3; 2,93 Ghz), 8 Gb RAM DDR-3 1.333 Mhz. I guess this configurations is enough to run FB without bottlenecks (to about 120 clients). You agree?

But the disks config are driving me crazy. I can't decide between standart HDD (SAS 15K rpm) or SSD (SATA-2). I initially wanted a simple RAID-1 array with 2 HDD SAS 15k rpm.

But, a great guy from the FB team development, with whom I keep in touch, thel this about RAID-1:

> approximately 70% faster reads compared with single disk.
> On the other hand, writes run aprox 20% slower.

After all, my problem with forced writes is just with writes. So, RAID-1 doesn't help. This way, I guess the RAID 10 (or RAID 1+0 as you prefer) can compensate the writes downfall, by the stripping technique.

Assuming to be truth the gain of the SSD over HDD, the better choice would be 4 SSD disks in a RAID 10 array.

But, this drives are still so many expensive (at least here), and I have to manage costs and performance, hitting on first shot. So, 4 SSD isn't an option and I must to decide between two basic configuration: 4 HDD SAS in RAID 10 arrange or 2 SSD in RAID 1 arrange.

I have few informations about benchmarking between SSD x HDD and lacks me more details about SSD performance. So, It's kind difficult to decide with so few informations and no chance to do a lab.

A Dell white paper about their SSD x HDD tells this:

> SSD's provide performance improvements up to forty to fifty times
> (40X‐50X) faster than enterprise class 15K RPM hard drives in
> customer applications that have high random I/O (input/output)
> requirements

However, further the same paper says:

> Customer applications with the most random data requirements
> will see the greatest benefit from SSD's over hard disk drives.
> Customers with highly sequential data will see very little
> performance benefit with SSD's over hard disk drives.

So two questions remains for me:

a) Considering a dedicated server that runs only FB, is the data requirements more random or sequential?

b) Considering all stuffs above, in my shoes, what disk config you **personally** choose in view to improve writes performance: 4 HDD SAS in RAID 10 or 2 SDD SATA in RAID 1?

Thanks for anyone that can help me.