ning Posted December 5, 2016 Share Posted December 5, 2016 hi, I have an OPI pc with armbian (legacy kernel), plan to set it as NAS. due to it has 4 USB ports without internal hub, so I decide to connect 3 USB HDD to it, and create a LVM+RAID5. but unfortunately, OPI pc can only recognize 2 USB HDD(any 2 of these 3 USB hdd), at any USB ports, the 3rd USB HDD can be found by lsusb but stops at "spinning up...." no /dev/sdc. but if I insert an USB disk, (with 2 USB HDD already inserted), it can be recognized and /dev/sdc is created. I guess whether there is a power supply issue. can this be fixed by USB HDD with additional power supply? is that right? Link to comment Share on other sites More sharing options...
tkaiser Posted December 5, 2016 Share Posted December 5, 2016 Yes, this is a power supply issue. And the whole idea is insane and just a waste of ressources. RAID5 is crap, especially when combining a lot of unreliable hardware. If you really care about availability better use vanilla kernel and a btrfs mirror (way better than mdraid these days) but if you care about data security/reliability then start to care also about data integrity, use one disk with btrfs for your data and another larger one for backup (read as: doing btrfs snapshots and sending them to the other device). Link to comment Share on other sites More sharing options...
ning Posted December 5, 2016 Author Share Posted December 5, 2016 thank you. you are right, combining a lot of unreliable hardware is not a good ideal. right now, I have setup LVM stripped volume for two USB HDD. for date integrity, i plan to use another disk to backup data.. Link to comment Share on other sites More sharing options...
tkaiser Posted December 5, 2016 Share Posted December 5, 2016 right now, I have setup LVM stripped volume for two USB HDD. If I were you I would take latest vanilla beta image from http://image.armbian.com/betaimages/ and then stop using stuff from last decade (mdraid, LVM) but rely on better stuff. I don't see the need for a stripe (RAID-0) here since OPi PC has just Fast Ethernet so you will always be bottlenecked by networking but by using btrfs you could use a combination of stripe and mirror: Striped data and mirrored metadata. Since btrfs uses checksums this allows to reliably check for data integrity even with a stripe for data: mkfs.btrfs -m raid1 -d raid0 /dev/sda /dev/sdb You can then run regular scrubs and get a warning if data got corrupted since checksums are mirrored on both drives. Does not protect against failing drives but using a 3rd drive to store snapshots (backup) is a good way to deal with this since most reasons for data loss are not dying disks but simple mistakes. Anyway: I would avoid RAID at all since the only purpose is increased availability and that's a joke with this kind of hardware anyway. If it's about data and not 99.99999% availability choosing a good backup strategy and looking after data integrity is always the better choice. 1 Link to comment Share on other sites More sharing options...
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