UPS does not protect against the tech behind the rack unplugging the
power cable, or an accidental power cycle from exercising the wrong
switch. Both are probably more common causes of failure than a total
power outage.

Erik Myllymaki wrote:
> I have been in discussion with 3ware support and after adjusting some
> settings, the 3ware card in RAID 1 gets better performance than the
> single drive. I guess this had everything to do with the write (and
> maybe read?) cache.
>
> Of course now i am in a dangerous situation - using volatile write
> cache without a BBU.
>
> If I were to use a UPS to ensure a soft shutdown in the event of power
> loss, am I somewhat as safe as if I were to purchase a BBU for this
> RAID card?
>
>
>
> Thanks.
>
> Mark Lewis wrote:
>> It's also possible that the single SATA drive you were testing (or the
>> controller it was attached to) is lying about fsync and performing write
>> caching behind your back, whereas your new controller and drives are
>> not.
>>
>> You'll find a lot more info on the archives of this list about it, but
>> basically if your application is committing a whole lot of small
>> transactions, then it will run fast (but not safely) on a drive which
>> lies about fsync, but slower on a better disk subsystem which doesn't
>> lie about fsync.
>>
>> Try running a test with fsync=off with your new equipment and if it
>> suddenly starts running faster, then you know that's the problem.
>> You'll either have a choice of losing all of your data the next time the
>> system shuts down uncleanly but being fast, or of running slow, or of
>> fixing the applications to use chunkier transactions.
>>
>> -- Mark
>>
>> On Fri, 2006-04-28 at 13:36 -0400, Vivek Khera wrote:
>>> On Apr 28, 2006, at 11:37 AM, Erik Myllymaki wrote:
>>>
>>>> When I had this installed on a single SATA drive running from the
>>>> PE1800's on-board SATA interface, this operation took anywhere
>>>> from 65-80 seconds.
>>>>
>>>> With my new RAID card and drives, this operation took 272 seconds!?
>>> switch it to RAID10 and re-try your experiment. if that is fast,
>>> then you know your raid controller does bad RAID5.
>>>
>>> anyhow, I have in one server (our office mail server and part-time
>>> development testing box) an adaptec SATA RAID from dell. it is
>>> configured for RAID5 and does well for normal office stuff, but
>>> when we do postgres tests on it, it just is plain old awful.
>>>
>>> but I have some LSI based cards on which RAID5 is plenty fast and
>>> suitable for the DB, but those are SCSI.
>>>
>>> For what it is worth, the Dell PE1850 internal PERC4/Si card is
>>> wicked fast when hooked up with a pair of U320 SCSI drives.
>>>
>>>
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