On 26/10/17 02:10 PM, jdd@dodin.org wrote:
this setup is extremely expensive and is interesting is you want a system as much as possible always running.
Once upon a time labour - man power - was cheap and equipment expensive. These days it is the other way round. Because of that we cost things in terms of time and effort. Work out the cost of downtime in term of human inconvenience. Even a day at minimum wage is more than the local street price of a 1T drive here. Sysadmins might be paid more than the cost of a 1T drive per hour. At that price point, if you can save an hour's time by using, as per points out, with a simple RAID1, mirroring, then you're winning. Then again, there are hybrid version of RAID, RAID6, multi-level versions such as RAID60, RAID100, ways of trading space efficiency, fault tolerance, ... There are also collection that aren't termed RAID but offer similar kinds of functionality and don't require all drives to be the same size. You can do things like that with LVM and I understand it is possible with BtrFS. In addition, ZFS, which is sort of like BtrFS in its "one FS to rule them all" -- them being the disk drives - attitude towards drives, can achieve this sort of things as well. How "expensive" or not is up to the decision process, but it is an expense that needs to be compared to other expenses. https://en.wikipedia.org/wiki/ZFS#Software_RAID_using_ZFS You can do RAID-like things with LVM such as mirroring, striping. You are not limited to one drive. You can implement different policies for different file systems. LVM is great when you have a bunch of drives that are different sizes :-) RAID is simply and only a method to store your data safely whereas LVM is a software which can extend the performance of a RAID. RAID *can* be done in hardware whereas LVM is software. https://www.centos.org/docs/5/html/Cluster_Logical_Volume_Manager/LV_create.... Please note: you can create more than one mirror. See also: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/htm... for recovering from a mirror failure As for striping, you can do that with LVM and control the number of devices used in the striping, the interleaving. With LVM you can use stripe mapping across the drives as you would in RAID-0, with the capacity being the same as RAID-0. However, LVM allows you to also use the remaining space for additional volume groups. In the case of mdadm and software RAID-0 on Linux, you cannot grow a RAID-0 group. You can only grow a RAID-1, RAID-5, or RAID-6 array. This means that you can’t add drives to an existing RAID-0 group without having to rebuild the entire RAID group but having to restore all the data from a backup. However, with LVM you can easily grow a logical volume. But, you cannot use stripe mapping to add a drive to an existing striped logical volume because you can’t interleave the existing stripes with the new stripes. However you can extend a a LV with another ... and you can mix and match the degree of striping. And yes, you can create a LV that is BOTH mirrored and striped. It is just a matter of having enough drives :-) And they don't all have to be of the same size or geometry. -- A: Yes. > Q: Are you sure? >> A: Because it reverses the logical flow of conversation. >>> Q: Why is top posting frowned upon? -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org