Advertisement
Advanced thin client solution for Linux, based on Open Source. Mix Windows and Linux applications on the same desktop. V
| Weekly edition | Kernel | Security | Distributions | Search |
| Archives | Calendar | Subscribe | Write for LWN | LWN.net FAQ |
RAID array
RAID array
Posted Mar 19, 2008 21:51 UTC (Wed) by Cato (subscriber, #7643)In reply to: RAID array by clugstj
Parent article: On the vger.kernel.org outage
RAID is nowhere near as reliable in practice as it appears on paper - one example is that you frequently find, after a single disk (A) has failed, that another disk (B) 'fails during recovery' - in reality, some sectors on disk B failed first but on a sector that did not get read or written, so the bad sectors are only picked up during RAID recovery, which entails reading the whole of disk B and others. See http://www.nber.org/sys-admin/linux-nas-raid.html for coverage of some of these issues and how NetApp and others would cover them. Personally I would only use ZFS, NetApp or something similar that does a lot of media scrubbing, sector checksumming etc, in addition to basic RAID.
(Log in to post comments)
RAID array
Posted Mar 19, 2008 22:20 UTC (Wed) by quotemstr (subscriber, #45331) [Link]
We use 3ware controllers at work, which can be set up to automatically and periodically verify that no sectors ave failed. That feature has already saved us once.
RAID array
Posted Mar 19, 2008 23:38 UTC (Wed) by daniel (subscriber, #3181) [Link]
"Personally I would only use ZFS, NetApp or something similar that does a lot of media scrubbing, sector checksumming etc, in addition to basic RAID." Would that not be an admission of defeat for Linux?
RAID array
Posted Mar 20, 2008 22:29 UTC (Thu) by Cato (subscriber, #7643) [Link]
Yes, it means I could only use Linux currently for storage if I went for ZFS/FUSE. This is a significant weakness in the Linux story - perhaps btrfs will go some way to fixing this, but overall it seems that Linux RAID and associated sector-checksumming filesystems are a long way behind where it needs to be. I don't think this stuff is particularly hard to do, but it does require some focused work on btrfs and on RAID improvements, and there are patent risks due to the Sun/NetApp patent lawsuits, of course.
RAID array
Posted Mar 20, 2008 6:46 UTC (Thu) by pbrutsch (subscriber, #4987) [Link]
That is a very common feature, and most certaily not limited to 3ware! I have Areca, Adaptec, and LSI Logic RAID cards that can all do the same.
RAID array
Posted Mar 20, 2008 12:23 UTC (Thu) by wurtel (subscriber, #7155) [Link]
Linux software raid (md) can also check an array for problems, Debian offers to run a cronjob every month to do that, if you install mdadm. Coupled with SMART autotests you're pretty safe.
RAID array
Posted Mar 20, 2008 20:20 UTC (Thu) by hmh (subscriber, #3838) [Link]
If you want to be pretty safe, you'll need to test every *day*, not once a month. I know this from experience.
RAID array
Posted Mar 20, 2008 22:31 UTC (Thu) by Cato (subscriber, #7643) [Link]
This sounds like a useful media scrubbing feature. However, sector checksumming seems like it requires filesystem changes, and I've only seen that proposed in btrfs, which is in early development stages.