<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="generator" content="HTML Tidy for Windows (vers 25 March 2009), see www.w3.org">
<title></title>
</head>
<body>
Thanks to all those who replied (including off list).<br>
<br>
Someone reminded me that whilst the FlashSystem will support 512 and 4k blocks, it "prefers" 4k. Maybe there is a performance penalty for the smaller writes.<br>
<br>
Second, a flash update is always going to be read erase write.<br>
<br>
We don't get any choice with FlashSystem 900 on the RAID set - only RAID5 is available.<br>
<br>
Given we have two FlashSystems in two data centres, looks like we are going with 4k sectors and GPFS replication.<br>
<br>
I assume that creating several smaller LUNs on each FlashSystem in the same failure group is still preferable to one big LUN so we get more IO queues to play with?<br>
<br>
Simon<br>
<br>
-----Original Message-----<br>
<b>From: </b>Marc A Kaplan [<a href="mailto:makaplan@us.ibm.com">makaplan@us.ibm.com</a>]<br>
<b>Sent: </b>Wednesday, May 18, 2016 12:27 AM GMT Standard Time<br>
<b>To: </b>gpfsug main discussion list<br>
<b>Subject: </b>Re: [gpfsug-discuss] Flash for metadata<br>
<br>
<font size="2" face="sans-serif">I think there are two points here:</font><br>
<br>
<font size="2" face="sans-serif">A) RAID striping is probably a "loser" for GPFS metadata. </font><br>
<font size="2" face="sans-serif">B) RAID mirroring for your metadata may or may not be faster and/or more reliable than GPFS replication. Depending on your requirements and assumptions for fault-tolerance one or the other might be the winner.</font><br>
<br>
<font size="2" face="sans-serif">But .. if you're serious about performance - measure, measure, measure and pick the winner. (And we'd like to know what you found!)</font><br>
<font size="2" face="sans-serif">And if you want the best performance, you'll probably need to (re)measure whenever you acquire new equipment.</font><br>
<br>
<font size="2" face="sans-serif">GPFS can do and does striping for high performance when reading and writing metadata and data...<br>
</font><br>
</body>
</html>