Re: Solid State Drives
- From: Mathias Magnusson <mathias.magnusson@xxxxxxxxx>
- To: vishal@xxxxxxxxxxxxxxx
- Date: Sun, 3 May 2009 11:38:56 +0200
I think we all can agree that the cost/benefit right now is hard to define.
I'm guessing that thought advanced ILM there are som use on the few blocks
in a database that gets the most activity.
Still the part of the OP's question I am most interested in, is the future
vision. How will the database world change when the price of SSD matches
that of harddisks? That day is sure to be here fairly soon and when that day
comes there will be probably few reasons to buy new harddisks,
The SAN cache changed some of the impact distribution on disk had for some
systems, the SSD will definately change a lot of things as all blocks on
them are created equal. The time cost for random versus sequential read will
probably not matter as much. My understanding is that all blocks are placed
in a somewhat random fashion on an SSD and new writes makes the block move
to a different physical location.
So does anyone have an idea for how old truths will change or even how
databases will adjust their algorithms for a day when harddisks are no
longer the cheapest way to store data? Or is the conclusion that SSD is a
fad that will fade into history over time? I cannot see that, but it would
be interesting to hear som arguments for it.
Mathias
http://mathiasmagnusson.com
http://blog.mathiasmagnusson.com
http://photo.mathiasmagnusson.com
http://oradbdev.mathiasmagnusson.com
On Sun, May 3, 2009 at 10:36 AM, Vishal Gupta <vishal@xxxxxxxxxxxxxxx>wrote:
> Tanel,
>
>
>
> I would agree. SAN cache does a pretty good job, even with RAID-5 as we
> have it in our bank.
>
>
>
> Since most of the data, most of time is getting written to memory (RAM) in
> SAN. And it offloaded to disk in the background by SAN. So database gets a
> success handshake as soon as data is written to SAN cache. And with
> combination of server RAM (i.e db cache) and SAN cache and RAID-5, reads are
> also lot faster. As Tanel, suggests idead should be to optimize your SQLs so
> they do less IO. But even if they cant, a full tablescan might get
> repeatedly served from SAN cache.
>
>
>
> Only problem I see with SAN cache is, there is no resource scheduling. Its
> all shared. So if you have too many system on same SAN cache, then one rouge
> system can bring down the entire company’s systems. I have seen that
> happening. If there is too much written to SAN cache and writes are coming
> fast and thick. Then SAN does not get time to offload this dirty cache to
> disk,and this write pending goes above your set threshold, it starts
> throttling writes from all the sources. And we had a linux kernel where it
> eventually made all the SAN connected mount point read-only. OUCH…. Major
> downtime on all systems. Now linux kernels have been patches so that mount
> point does not become read-only under such conditions.
>
>
>
> But SAN administrators really needs the understanding of databases IO, and
> also needs to be contain busy system to their own front end ports (Fibre
> channel ports) and their own disk and controllers.
>
>
>
> But still they don’t have the ability provided by SAN to isolate cache for
> a particular system. Or ability to throttle only selected systems/FC ports.
>
>
>
>
>
>
>
> Regards,
>
> Vishal Gupta
>
>
>
> *From:* oracle-l-bounce@xxxxxxxxxxxxx [mailto:
> oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Tanel Poder
> *Sent:* 01 May 2009 18:22
> *To:* dofreeman@xxxxxxxxxxx; 'Oracle-L'
> *Subject:* RE: Solid State Drives
>
>
>
> Once they get cheap and big then there would be a business case for them
> for regular shops.
>
>
>
> But right now, if you want to reduce the time spent waiting for physical
> reads in your database - one way is buy faster IO subsystem which SSD *may
> * give, another way is to just buy more memory for your server and do less
> physical reads. The same is with writes, consider whether its cheaper to
> buy/deploy/maintain the SSDs or just to have more write cache in your
> storage array (and again, if you buy more RAM into your server for caching
> read data then you can allocate even more of the storage cache for caching
> writes).
>
>
>
> So the question should be what's the most cost-effective option for
> achieving the result - reducing TIME spent doing physical IO. Given the
> write-caching of large storage arrays already in use in todays enterprises I
> don't think adding SSDs make sense from cost/performance perspective. Of
> course when the technology gets cheaper then the potential power savings and
> lesser drive dying rate will be another factor to consider.
>
>
>
> So my prediction is that, unless some other major new technology emerges in
> coming few years, SSDs will replace disk spindles for online "active" data
> just like (remote) disk spindles have replaced tape backups in some
> enterprises (btw I'm not saying that I like this approach entirely - tapes
> have the benefit of being physically disconnected from any servers, in a
> guarded safe in a bank in another city or so).
>
>
>
> In addition to backups, the disk spindles will still be used for
> archived data as well (lots of storage which is rarely accessed), they are
> faster than tape but cheaper per gigabyte than SSDs. Long term backups are
> kept on tapes, but some companies will completely throw away their tape
> systems to cut costs & complexity and keep all backups on disk spindles.
>
>
>
> After saying all that - currently I don't see much reason for buying SSDs
> for database solutions which are already deployed on mid/high-end storage
> arrays.
>
>
>
> --
> Regards,
> Tanel Poder
> http://blog.tanelpoder.com
>
>
>
>
> ------------------------------
>
> *From:* oracle-l-bounce@xxxxxxxxxxxxx [mailto:
> oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Freeman, Donald
> *Sent:* 01 May 2009 16:09
> *To:* Oracle-L (oracle-l@xxxxxxxxxxxxx)
> *Subject:* Solid State Drives
>
> Has anybody given any thought to where we are going as SSD's get cheaper
> and bigger? We've been going round and round at my shop with discussions
> about RAID, other disk allocation issues, fights over storage. I mean we
> seem to spend a lot of time on that issue. I saw that IBM is testing a 4 TB
> SSD. I was wondering if you'd have to mirror that, What kind of
> reliability we would be getting. No more RAID discussions? I've heard
> there is a finite number of times you can write to it. What's the upgrade
> path here?
>
>
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