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A Fasttrack, RAID, Linux, Windoze, Horror Story

July 11, 2007 – 8:37 am Print This Post

Posted 7/18/07 after a two week hardware ordeal with the server, UGH!:
Update: This is all a moot point now as I dumped Red Hat Fedora and moved to Debian. A much more friendly version of Linux for web hosting. But it’s here for historic purposes.

TUC is currently undergong some server upgrades. As a result the web gallery is currently unavailable. It should be up and running in a day or two…

fasttrack
 
 

After several hardware failures and six or seven mandriva, then Fedora reloads, it’s finally up for good. And a big Cheer for Fedora Core (Moonshine) at the moment, onwards and upwards as they say!

Regarding the Promise fasttrack 100 hardware RAID controller issue that caused me no end of grief… If reading this helps prevent grief for you, all the better.

I’ve learned that one cannot use a fasttrack controller reliably under Fedora Core with existing RAID partitions, (wind-woes) and removing them is even worse. I had to zero fill both drives to get them to work under linux. There is no other way (that I know) to remove the partition markings defining the drives as part of a hybrid RAID (Promise Fasttrack) controller format.

For what’s it’s worth, the fasttrack is a hardware implementation of software RAID. After learning and thinking a bit, it seems there is no reason to use such a setup. It already exists under linux and even in wind-woes. I also learned that the Fasttrack is not a full hardware implementation of RAID. It just maps every other sector times the stripe value to the “next” drive in an ongoing cycle. Not really any different than software raid under either windoes or linux except that it allows the bios to see both underlying drives, which is where the problem lies. It does, however, do the switching in hardware, marking the drives as part of a special RAID volume. There really is no reason for such a device now days. The original reason was to allow windows to boot a RAID volume. In windows, where only the driver sees the partitions it’s not a big deal, but under linux where lots of different things write directly to the hardware (hdparm), it’s a problem, a big problem. Some of them interpret the partition incorrectly and write things where they should not be written. I lost my Logical Volumes twice and the entire windows partition I was hoping to save. You can tell if it’s interpreting the volume as RAID if it shows up under /dev/mapper rather than /dev/hdx or /dev/sdx. Later version of Red Hat and Fedora use the SATA mapping rather than hdx, like earlier versions.

If I were to use any of the Promise Fasttrack controllers with fedora (or any linux OS), I’d make sure it is the only OS on the system and zerofill the drive ends before use and let Linux map the volume(s). Actually, I wouldn’t and now I don’t. The standard LV partition setup divides the drives just fine and while I don’t get 100 meg per second with it, I do get 55 stable and hard, which is really quite good for an old PIII coppermine @ just over 1G.

In case you’ve used or are using this setup, it may seem to be fine until you update your kernel or migrate to the next OS level. Then things get messed up, especially with Logical Volumes. The update goes smootly until it installs grub on the mbr when it seems to make some assumptions and reach across the partition boundary, changing something it shouldn’t, a bounds violation for sure, and in the process it destroys your entire logical volume making it unrecoverable unless you know exactly what got changed which implies you know what it should look like in magnetic pits, let alone how to restore it properly, you’re screwed. So, if you have a promise fasttrack 100 and want to use it with Fedora Core 6 or later, don’t. There is no performace gain at all. I got 45 MBPS using raid and 55 using partition mapping with a LV. :)

Thanks for your patience if you were reading things here and I apoligize if some of the articles got renumbered. I imported them from a backup so they should match the internet presch URL’s

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