Re: Reliability with RAID 10 SSD and Streaming Replication

Thank you for your advice guys. We'll definitely turn off init.d script for
PostgreSQL on the master. The standby host will be disk-based so it will be
less vulnerable to power loss.

I forgot to mention that we'll set up Wal-e <https://github.com/wal-e/wal-e> to
ship base backups and WALs to Amazon S3 continuous as another safety
measure. Again, the lost of a few WALs would not be a big issue for us.

Do you think that this setup will be acceptable for our purposes?

Thanks,
Cuong

On Fri, May 17, 2013 at 8:39 AM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> On Thu, May 16, 2013 at 11:46 AM, Merlin Moncure <mmoncure(at)gmail(dot)com>wrote:
>
>> On Thu, May 16, 2013 at 1:34 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>> > On Thu, May 16, 2013 at 7:46 AM, Cuong Hoang <climbingrose(at)gmail(dot)com>
>> wrote:
>> >>
>> >> Hi all,
>> >>
>> >> Our application is heavy write and IO utilisation has been the problem
>> for
>> >> us for a while. We've decided to use RAID 10 of 4x500GB Samsung 840
>> Pro for
>> >> the master server. I'm aware of write cache issue on SSDs in case of
>> power
>> >> loss. However, our hosting provider doesn't offer any other choices of
>> SSD
>> >> drives with supercapacitor. To minimise risk, we will also set up
>> another
>> >> RAID 10 SAS in streaming replication mode. For our application, a few
>> >> seconds of data loss is acceptable.
>> >>
>> >> My question is, would corrupted data files on the primary server affect
>> >> the streaming standby? In other word, is this setup acceptable in
>> terms of
>> >> minimising deficiency of SSDs?
>> >
>> >
>> >
>> > That seems rather scary to me for two reasons.
>> >
>> > If the data center has a sudden power failure, why would it not take out
>> > both machines either simultaneously or in short succession? Can you
>> verify
>> > that the hosting provider does not have them on the same UPS (or even
>> worse,
>> > as two virtual machines on the same physical host)?
>>
>> I took it to mean that his standby's "raid 10 SAS" meant disk drive
>> based standby.
>
>
> I had not considered that. If the master can't keep up with IO using
> disk drives, wouldn't a replica using them probably fall infinitely far
> behind trying to keep up with the workload?
>
> Maybe the best choice would just be stick with the current set-up (one
> server, spinning rust) and just turn off synchrounous_commit, since he is
> already willing to take the loss of a few seconds of transactions.
>
> Cheers,
>
> Jeff
>