Re: WAL and O_DIRECT

>> However our DB2 folks are raising a concern that PG WAL writes may not be crash safe, unless we are using
>> write back technology in SAN or SSD , which we are using.

> What's your point exactly?  If the underlying hardware does not provide durable writes, there's
> nothing PG (or DB2) can do to fix that.

Am I right in concluding that PG WAL writes without underlying h/w caching is not crash proof. 
Fortunately these days caching is  ubiquitous in all SSD/SAN technology. Both Oracle and DB2 always open WAL 
logs in O_DIRECT. Is this thinking outdated with modern technology which caches writes. Wonder why Oracle/DB2 
are not making O_DIRECT optional. I am sure it will increase the write performance.