[CentOS] Upgrading system from non-RAID to RAID1

Thu Jan 12 06:43:52 UTC 2023
Simon Matter <simon.matter at invoca.ch>

> On 01/11/2023 02:09 AM, Simon Matter wrote:
>> What I usually do is this: "cut" the large disk into several pieces of
>> equal size and create individual RAID1 arrays. Then add them as LVM PVs
>> to
>> one large VG. The advantage is that with one error on one disk, you wont
>> lose redundancy on the whole RAID mirror but only on a partial segment.
>> You can even lose another segment with an error on the other disk and
>> still have redundancy if the error is in another part.
>> That said, it's a bit more work to setup but has helped me several times
>> in the decades ago.
> But is your strategy of dividing the large disk into individual RAID1
> arrays also applicable to SSDs? I have heard, perhaps incorrectly, that
> once a SSD fails, the entire SSD becomes unusable which would suggest that
> dividing it into multiple RAID1 arrays would not be useful?

What you heard seems extremely oversimplified to me. A HD can fail in
different manners and so can SSDs.
Anyway, the splitting of large disks has additional advantages. Think of
what happens in case of a failure (power loss, kernel crash...). With the
disk as one large chunk, the whole disk has to be resynced on restart
while with smaller segments only those which are marked as dirty have to
be resynced. This can make a bit difference.