RE: Solid State Drives
Date: Sat, 2 May 2009 17:51:12 +0300
Whatever the external device is based on (flash or plain RAM) - it is probably cheaper and faster to have more RAM for the server itself than that RAM in some external device.
And talking about Oracle databases:
- As far as undo is considered, it's definitely cheaper to keep it in buffer cache than ping it in and back from external device (you have logical IOs + physical IOs + external bus traffic versus just logical IOs in case of buffer cache)
- As far as temp tablespaces are concerned, it's definitely cheaper to keep the sort+hash data in PGAs and temp tables in buffer cache, for above mentioned reasons.
- As far as redo writes are concerned the storage array write cache should take care of it and consolidate the small writes into larger ones. I haven't seen a corporation for years who'd run their database on an array *without* write caching ability. You just need to configure your cache right that it wouldn't be polluted by unneccessary stuff by other systems and reads (basically set write cache as a large portion of storage array cache and leave only a little for reads - as read cache should reside in server RAM - buffer cache).
My point here is - yes, adding SSDs to storage array *can* help, but adding *RAM* to servers can help more, it's cheaper, faster and involves less complexity. Of course someone might say that "hey my little dual-CPU pizza box server doesn't support more than 8GB of memory and that's why I need SSD"... um... it's time to buy a real server first in this case. A single DL785 supports up to 512GB of RAM for example.
-- Regards, Tanel Poder http://blog.tanelpoder.comReceived on Sat May 02 2009 - 09:51:12 CDT
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Mark W. Farnham
> Sent: 02 May 2009 15:46
> To: tanel_at_poderc.com; jeremy.schneider_at_ardentperf.com;
> Cc: andrew.kerber_at_gmail.com; dofreeman_at_state.pa.us;
> Subject: RE: Solid State Drives
> We seem to have adopted an SSD==Flash assumption on this
> thread. Given the faster cost drop in flash than in other
> types of solid state memory, that may be appropriate. Still
> there are other choices and whether they are economic or not
> going forward, it has long been the case that if you really
> needed isolated throughput to persistent storage for modest