RE: Solid State Drives

From: Tanel Poder <>
Date: Sat, 2 May 2009 17:51:12 +0300
Message-ID: <8D83B08F0C92466E9162C232352F8CCE_at_porgand>

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:

  1. 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)
  2. 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.
  3. 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.

Tanel Poder

> -----Original Message-----
> From:
> [] On Behalf Of Mark W. Farnham
> Sent: 02 May 2009 15:46
> To:;;
> Cc:;;
> 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
Received on Sat May 02 2009 - 09:51:12 CDT

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