On Fri, Mar 13, 2015 at 7:55 AM, Achilleas Mantzios
<achill@matrix.gatewaynet.com> wrote:
> On 13/03/2015 15:47, Scott Marlowe wrote:
>>
>> On Fri, Mar 13, 2015 at 7:16 AM, Achilleas Mantzios
>> <achill@matrix.gatewaynet.com> wrote:
>>>
>>> On 13/03/2015 13:40, Joshua D. Drake wrote:
>>>>
>>>> On 03/13/2015 04:27 AM, Achilleas Mantzios wrote:
>>>>>
>>>>>
>>>>> Hello,
>>>>>
>>>>> we maintain a DB of nearly 500GB of data (and always getting larger),
>>>>> and we are currently thinking of moving to SSD.
>>>>> I have read Greg Smith's book on PostgreSQL 9.0 High Performance and
>>>>> his
>>>>> considerations on SSD and the way that write back works.
>>>>>
>>>>> This particular model (Samsung SSD 850 PRO 1T) does not employ any
>>>>> special circuitry, battery or capacitor
>>>>> to enforce that the data are really flushed to the medium.
>>>>>
>>>>> What is your take on this? Is it dangerous to have PgSQL on this disk
>>>>> especially in cases of power outages? (we have full UPS support,
>>>>> however
>>>>> nothing can be overlooked, anything can happen)
>>>>
>>>>
>>>> If it does not have power loss protection, don't use it.
>>>
>>>
>>> Thanx Joshua.
>>>
>>> If theoretically somehow we eliminate the power loss factor, would it
>>> make
>>> sense to use such a disk?
>>
>> Sadly there's no way to eliminate power loss in real life.
>>
>> Now if you can live with some data loss corruption that's a different
>> matter.
>
>
> Thanx,
> the question is if postgresql will recover, we can tolerate some data loss,
> but no total db corruption, equivalent to fsync=false, with the db unable to
> recover.
>
Sadly that is the exact thing that is likely to happen.
P.s. I worked in a BIG data center that lost all power. Three power
conditioners, three USPs and the switch for the diesel gen all blew
out at once. Lots of dbs that relied on never losing power were
corrupted and took days to recover most of their data and get back
online.