Bug 234110
Summary: | RAID5 on 2 disks | ||||||
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Product: | [Fedora] Fedora | Reporter: | Eli <elicarter> | ||||
Component: | anaconda | Assignee: | Anaconda Maintenance Team <anaconda-maint-list> | ||||
Status: | CLOSED WONTFIX | QA Contact: | |||||
Severity: | medium | Docs Contact: | |||||
Priority: | medium | ||||||
Version: | 6 | Keywords: | Reopened | ||||
Target Milestone: | --- | ||||||
Target Release: | --- | ||||||
Hardware: | All | ||||||
OS: | Linux | ||||||
Whiteboard: | |||||||
Fixed In Version: | Doc Type: | Bug Fix | |||||
Doc Text: | Story Points: | --- | |||||
Clone Of: | Environment: | ||||||
Last Closed: | 2007-04-02 18:40:39 UTC | Type: | --- | ||||
Regression: | --- | Mount Type: | --- | ||||
Documentation: | --- | CRM: | |||||
Verified Versions: | Category: | --- | |||||
oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |||||
Cloudforms Team: | --- | Target Upstream Version: | |||||
Embargoed: | |||||||
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Description
Eli
2007-03-27 03:27:05 UTC
We don't support doing degraded RAIDs like this because people would expect to get the benefit of the RAID and then file bugs when they didn't. While I can see some use cases for setting up degraded RAIDs, that's not what I was trying to propose. RAID5 with 2 disks gives you the same redundancy as RAID1, but with the ability to add disks later. 2 x 400GB drives, RAID5'ed gives you 400GB of usable space, and if either fail, you're ok. Same as RAID1. But you can add disks to a RAID5 with mdadm --grow. So I could add a third 400GB drive to the 2x400 RAID5, and my usable capacity will grow from 400GB to 800GB. I can't do that with RAID1. http://www.acnc.com/04_01_05.html Where's your parity disk with only 2 drives? We cannot support a scenario like this during installation. Closing as WONTFIX. Created attachment 151341 [details]
Test case to demonstrate the viability of 2-disk RAID5
"Where's your parity disk with only 2 drives?" Spread across the two drives, just like it's spread across three drives. Using the same diagram style as the link you provided: 3-disk case: disk0 | disk1 | disk2 A1 B1 P1 A2 P2 C2 P3 B3 C3 2-disk case: disk0 | disk1 A1 P1 P2 B2 A3 P3 Please look at the test case I attached as a demonstration of the validity of this configuration. If there is something wrong with the test case, please point it out. Test case requirements: - must be run as root - uses 200MB of disk space - uses /dev/md0, /dev/loop0, and /dev/loop1 - takes 1 minute 20 seconds to run on my 2.6GHz notebook I fail to see the advantage to RAID 5 on two disks. You mention the only advantage you want is the ability to grow the array a year or so down the road when you need 800GB of storage space. That's some serious planning going on, but do you not forsee yourself reinstalling in that timeframe or upgrading or even switching to new hardware? Maybe not, I dunno. Also, the performance hit you take with RAID 5 vs. straight up mirroring when you only have two drives seems like a waste of resources. For that year of time before you need more space, why not running mirroring and take the best performance you can get given the hardware you have? By definition, RAID 5 with fewer than three disks is in a degraded state and we're not going to support these scenarios during installation via anaconda. If you absolutely need this for your environment, consider a kickstart file tailored to your environment. |