RE: [Exadata] How do you use FlashDisk ?
Date: Sat, 19 Mar 2011 19:29:32 +0100
Message-ID: <4814386347E41145AAE79139EAA398981500889BD2_at_ws03-exch07.iconos.be>
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_at_uptime.be
tel +32(0)3 451 23 82
http://www.uptime.be
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From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Robert Freeman
Sent: zaterdag 19 maart 2011 14:59
To: surachart_at_gmail.com; Oracle-L_at_freelists.org
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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Received on Sat Mar 19 2011 - 13:29:32 CDT