Ram disks, definately. ;-) Afraid I'm still going with diskless nodes. You save 1. some money on the disks themselves 2. more money on solving disk failures 3. yet more money on cooling
This may be specially important in a high-density rack situation, where if you get the disks out of the way each box can get more ventilators up front as well as in the rear. On the other hand, Windows Vista has had its uses(!), such as driving RAM prices down as demand expands ... Cheers, -Alan -----Original Message----- From: [EMAIL PROTECTED] on behalf of Jon Forrest Sent: Mon 9/29/2008 6:44 AM To: Beowulf Mailing List Subject: [Beowulf] Compute Node OS on Local Disk vs. Ram Disk There are two philosophies on where a compute node's OS and basic utilities should be located: 1) On a local harddrive 2) On a RAM disk I'd like to start a discussion on the positives and negatives of each approach. I'll throw out a few. Both approaches require that a compute node "distribution" be maintained on the frontend machine. In both cases it's important to remember to make any changes to this distribution rather than just using "pdsh" or "tentakel" to dynamically modify a compute node. This is so that the next time the compute node boots, it gets the uptodate distribution. Although the mechanism for maintaining the distribution varies in either approach, I consider this a push since one mechanism isn't inherently better than the other. Assuming the actual OS image is the same in both cases, #2 clearly requires more memory than #1. There are actually two approaches to #2 - a) where only the OS and other stuff necessary to boot the system are kept in memory and everything else is in an NFS-mounted file system, and b) where the whole OS installation is kept in memory. Depending on which approach is taken, the RAM-based installations can take hundreds of MB more than a local harddrive installation. However, on a modern multicore compute node this might just be a few percent of the total RAM on the node. Long ago not installing a local harddrive saved a considerable about of money but this isn't true anymore. Systems that need to page (or swap) will require a harddrive anyway since paging over the network isn't fast enough so very few compute nodes will be running diskless. Approach #2 requires much less time when a node is installed, and a little less time when a node is booted. What are some of your favorite issues, positive or negative, with each approach? Cordially, -- Jon Forrest Research Computing Support College of Chemistry 173 Tan Hall University of California Berkeley Berkeley, CA 94720-1460 510-643-1032 [EMAIL PROTECTED] _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
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