Re: Question about configuration and SSD

On 02/06/11 18:53, Craig Ringer wrote:
> On 02/06/11 16:26, Szymon Guz wrote:
>> Hi,
>> do we need some special configuration for SSD drives, or is that enough
>> to treat those drives normally?
>
> Make sure the SSDs have a supercapacitor or battery backup for their
> write cache. If they do not, then do not use them unless you can disable
> write caching completely (probably resulting in horrible performance),
> because you WILL get a corrupt database when power fails.
>
> If the SSDs have a supercap or a battery backed write cache so that they
> can guarantee that all cached data will be written out if the power goes
> down, you won't need any special configuration. You may want to tune
> differently for best performance, though - for example, reducing
> random_page_cost .

Are you sure?

SSDs support barriers and "fsync" just like regular hard drives, and
your regular Linux filesystems will ensure things are committed to disk.

Rather I would say - if you have an SSD *with*
battery-or-capacitor-backed write-cache, then disable "Barriers" and
enable writeback mode on your filesystem - and get a huge performance
increase.

But if you don't have those features, then just use your filesystem with
the normal settings.. and it'll still be a lot faster than regular
hard-drives, and just as safe.

-Toby