Re: Test disk reliability (or HGST HTS721010A9E630 surprisingly reliable)

On 12/21/15 8:22 AM, Bill Moran wrote:
>>> Why? Just because a disk isn't enterprise-grade doesn't mean it has to lie
>>> > >about fsync, which is the only thing diskchecker.pl tests for.
>>> > >
>> >
>> >I was thinking that since the disk have a 32M write-cache (with not
>> >battery) it would lie to the OS (and postgres) about when data are really
>> >on disk (not in the disk write cache). But maybe that thinking was wrong.

There are ways to make on-disk write caches safe without a battery. IIRC
some hard drives would use the inertia of the platter (turning the motor
into a generator) to write contents out on power-off. You could also use
a "super cap".

> It varies by vendor and product, which is why diskchecker.pl exists.
> It's even possible that the behavior is configurable ... check to see
> if the vendor provides a utility for configuring it.

Your OS might let you control it too; I know FreeBSD has support for
this. (Whether the drive obeys or not is a different matter...)
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com