Hello, Just a couple questions regarding RAID. Here's thesituation. I bought a 4TB drive before I upgraded from 6.8 to 7.3. I'm not too far into this that Ican't start over. I wanted disk space to backup 3 other machines. I way overestimated what I needed for full, incremental and image backups with UrBackup.I've used less than 1TB so far. I would like to add an additional drive to makeit a RAID server. I may use a PCIe SSD for the boot drive if I can find onecompatible with my old hardware. 1- Better to go with a hardware RAID (mainboardsupported) or software? 2 - Can an existing drive with data on it be used as aRAID drive without losing current data? 3 - Can additional drive(s) be added later with a changein RAID level without current data loss? TIA
On 2/14/2017 4:48 PM, tdukes at palmettoshopper.com wrote:> 1- Better to go with a hardware RAID (mainboardsupported) or software?I would only use hardware raid if its a card with battery (or supercap+flash) backed writeback cache, such as a megaraid, areca, etc. otherwise I would use mdraid mirroring.> 2 - Can an existing drive with data on it be used as aRAID drive without > losing current data?software mdraid will let you add a mirror to an existing disk. or if its using LVM, you can mirror in LVM now.> 3 - Can additional drive(s) be added later with a changein RAID level > without current data loss?Only some systems support that sort of restriping, and its a dangerous activity (if the power fails or system crashes midway through the restriping operation, its probably not restartable, you quite likely will lose the whole volume)... with LVM mirroring, you can add more pairs of drives as additional mirrors to the volume group. -- john r pierce, recycling bits in santa cruz
On 14/02/17 07:58 PM, John R Pierce wrote:> On 2/14/2017 4:48 PM, tdukes at palmettoshopper.com wrote: >> 1- Better to go with a hardware RAID (mainboardsupported) or software? > > I would only use hardware raid if its a card with battery (or > supercap+flash) backed writeback cache, such as a megaraid, areca, etc. > otherwise I would use mdraid mirroring. > > >> 2 - Can an existing drive with data on it be used as aRAID drive without >> losing current data? > > software mdraid will let you add a mirror to an existing disk. or if > its using LVM, you can mirror in LVM now.Note; If you're mirroring /boot, you may need to run grub install on both disks to ensure they're both actually bootable (or else you might find yourself doing an emergency boot off the CentOS ISO and installing grub later).>> 3 - Can additional drive(s) be added later with a changein RAID level >> without current data loss? > > Only some systems support that sort of restriping, and its a dangerous > activity (if the power fails or system crashes midway through the > restriping operation, its probably not restartable, you quite likely > will lose the whole volume)... with LVM mirroring, you can add more > pairs of drives as additional mirrors to the volume group. > >-- Digimer Papers and Projects: https://alteeve.com/w/ "I am, somehow, less interested in the weight and convolutions of Einstein?s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops." - Stephen Jay Gould
On 2017-02-15, John R Pierce <pierce at hogranch.com> wrote:> On 2/14/2017 4:48 PM, tdukes at palmettoshopper.com wrote: > >> 3 - Can additional drive(s) be added later with a changein RAID level >> without current data loss? > > Only some systems support that sort of restriping, and its a dangerous > activity (if the power fails or system crashes midway through the > restriping operation, its probably not restartable, you quite likely > will lose the whole volume)Doesn't mdraid support changing RAID levels? I think it will even do it reasonably safely (though still better not to have a power failure!). I have a vague memory of adding a drive to a RAID5 and converting it to a RAID6 but I could be misremembering. --keith -- kkeller at wombat.san-francisco.ca.us