Re: [BackupPC-users] Centralized storage with multiple hard drives

Holger Parplies <wbppc AT parplies DOT de> wrote on 03/19/2014 07:26:02 PM: > Les Mikesell wrote on 2014-03-19 11:25:38 -0500 [Re: [BackupPC- > users] Centralized storage with multiple hard drives]: > > Throwing RAM at a disk performance problem usually helps. > > You've used BackupPC before, Les, right? ;-) > BackupPC prefers pool reads over writes when possible, and it typically > accesses large amounts of data almost randomly. Caching metadata will help, > caching data likely won't.

I've given up explaining this to Mr. Mikesell. I've posted info to the list several times showing the performance on BackupPC servers that had 512MB (Megabytes) of RAM. Zero swapping, and something like 300MB used for caching. I have then upgraded them to 4GB of RAM (8 times as much RAM!) and saw a whopping 15 or so minutes savings on a backup that took 10 to 12 hours. (In fact, the only real reason I use 4GB minimum across the board now is that I ran into a problem where a fsck wouldn't complete without more RAM.)

> > As does not using raid5. > > One disk per client host sort of precludes raid5 ;-).

And I haven't seen that RAID-5 has been that much of an issue. As you mention, BackupPC is *READ* heavy so the RMW penalty doesn't hurt much. My experience with both RAID-5 *AND* RAID-6 (even software RAID-6!) is just fine. Of course, I have a minimum of 4 drives in a RAID array (6 minimum for RAID-6), so I'm usually bottlenecked somewhere else anyway, such as a single 1Gb link. It's not hard to mange writing 70MB/s of data!

Tim Massey


Out of the Box Solutions, Inc. Creative IT Solutions Made Simple! http://www.OutOfTheBoxSolutions.com tmassey AT obscorp DOT com		22108 Harper Ave. St. Clair Shores, MI 48080 Office: (800)750-4OBS (4627) Cell: (586)945-8796

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