RE: [Exadata] How do you use FlashDisk ?
- From: D'Hooge Freek <Freek.DHooge@xxxxxxxxx>
- To: "robertgfreeman@xxxxxxxxx" <robertgfreeman@xxxxxxxxx>, "surachart@xxxxxxxxx" <surachart@xxxxxxxxx>, "Oracle-L@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Sat, 19 Mar 2011 19:29:32 +0100
Didn't Oracle add a write cache on the flash cards to make writes on flashdisks
go faster?
Off course, when doing large sequentials writes that write cache will not help
you much.
Regards,
Freek D'Hooge
Uptime
Oracle Database Administrator
email: freek.dhooge@xxxxxxxxx
tel +32(0)3 451 23 82
http://www.uptime.be
disclaimer: www.uptime.be/disclaimer
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From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Robert Freeman
Sent: zaterdag 19 maart 2011 14:59
To: surachart@xxxxxxxxx; Oracle-L@xxxxxxxxxxxxx
Subject: Re: [Exadata] How do you use FlashDisk ?
Flash disks for WRITE operations are actually not that fast. I don't have the
performance numbers here, but you really don't buy anything in terms of write
performance with flash disks. So I would not recommend them for a disk group
that will contain, say, online redo logs.
Also, with the Flash on Exadata keep in mind that it's a write through flash.
Thus, the data cached in Flash is not based on what is written to the disks or
read from them, but rather there is an algorithm that Oracle uses to determine
what is put in flash and what is not. For example, large table scan blocks or
large table loads are NOT going to to populate the flash cache, whereas
frequently used blocks will. This makes the flash disks very much one of the
key ingredients for the OLTP performance that we get on Exadata.
Cheers!
Robert G. Freeman
Master Principal Consultant, Oracle Corporation, Oracle ACE
Author of various books on RMAN, New Features and this shorter signature line.
Blog: http://robertgfreeman.blogspot.com
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