Re: Reliability with RAID 10 SSD and Streaming Replication

Hi Tomas,

We have a lot of small updates and some inserts. The database size is at
35GB including indexes and TOAST. We think it will keep growing to about
200GB. We usually have a burst of about 500k writes in about 5-10 minutes
which basically cripples IO on the current servers. I've tried to increase
the checkpoint_segments, checkpoint_timeout etc. as recommended in
"PostgreSQL 9.0 Performance" book. However, it seems like our server just
couldn't handle the current load.

Here is the server specs:

Dual E5620, 32GB RAM, 4x1TB SAS 15k in RAID10

Here are some core PostgreSQL configs:

shared_buffers = 2GB # min 128kB
work_mem = 64MB # min 64kB
maintenance_work_mem = 1GB # min 1MB
wal_buffers = 16MB
checkpoint_segments = 128
checkpoint_timeout = 30min
checkpoint_completion_target = 0.7

Thanks,
Cuong

On Fri, May 17, 2013 at 10:06 AM, Tomas Vondra <tv(at)fuzzy(dot)cz> wrote:

> Hi,
>
> On 16.5.2013 16:46, Cuong Hoang 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
>
> What does "heavy write" mean in your case? Does that mean a lot of small
> transactions or few large ones?
>
> What have you done to tune the server?
>
> > 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.
>
> Streaming replication allows zero data loss if used in synchronous mode.
>
> > 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?
>
> It should be.
>
> Have you considered using a UPS? That would make the SSDs about as
> reliable as SATA/SAS drives - the UPS may fail, but so may a BBU unit on
> the SAS controller.
>
> Tomas
>
>
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