Re: Specifications for a new server

Since the commitlog/WAL is sequential-write, does it mattert that much to
put it in ssd ?(i understand that it matters to put it in separate
disk-subsystem so the write/read patterns don't interfere)

On Tue, May 6, 2014 at 1:07 PM, Michael Stone <mstone+postgres(at)mathom(dot)us>wrote:

> On Tue, May 06, 2014 at 11:13:42AM +0200, Johann Spies wrote:
>
>> Analysis or the SAR-logs showed that there were too much iowait in the
>> CPU's on
>> the old system which has a lower spec CPU than the ones considered for
>> the new
>> system.
>>
>
> iowait means the cpu is doing nothing but waiting for data from the disk.
> buying faster cpus means that they will be able to spend more time waiting
> for data from the disk. you'd probably get much better bang for the buck
> upgrading the storage subsystem than throwing more money at cpus.
>
>
> We are looking possibly the following hardware:
>>
>> CPU: 2 x Ivy Bridge 8C E5-2667V2 3.3G 25M 8GT/s QPI - 16 cores
>> RAM: 24 x 32GB DDR3-1866 2Rx4 LP ECC REG RoHS - 768Gb
>>
>> with enough disk space - about 4.8 Tb on RAID 10.
>> My question is about the possible advantage and usage of SSD disks in the
>> new
>> server.
>>
>
> At the moment I am considering using 2 x 200GB SSD' s for a separate
>> partion for temporary files and 2 x 100GB for the operating system.
>>
>
> If you're talking about SSDs for the OS, that's a complete waste; there is
> essentially no I/O relating to the OS once you've booted.
>
>
> So my questions:
>>
>> 1. Will the SSD's in this case be worth the cost?
>> 2. What will the best way to utilize them in the system?
>>
>
> The best way to utilize them would probably be to spend less on the CPU
> and RAM and more on the storage, and use SSD either for all of the storage
> or for specific items that have a high level of I/O (such as the indexes).
> Can't be more specific than that without a lot more information about the
> database, how it is utilized, and what's actually slow.
>
> Mike Stone
>
>
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