[CentOS] raid 5 install

[Warren Young]

On Jul 1, 2019, at 8:26 AM, Valeri Galtsev <galtsev at kicp.uchicago.edu> wrote:
> 
> RAID function, which boils down to simple, short, easy to debug well program.

RAID firmware will be harder to debug than Linux software RAID, if only because of easier-to-use tools.

Furthermore, MD RAID only had to be debugged once, rather that once per company-and-product line as with hardware RAID.

I hope you’re not assuming that hardware RAID has no bugs.  It’s basically a dedicated CPU running dedicated software that’s difficult to upgrade.

> if kernel (big and buggy code) is panicked, current RAID operation will never be finished which leaves the mess.

When was the last time you had a kernel panic?  And of those times, when was the last time it happened because of something other than a hardware or driver fault?  If it wasn’t for all this hardware doing strange things, the kernel would be a lot more stable. :)

You seem to be saying that hardware RAID can’t lose data.  You’re ignoring the RAID 5 write hole:

    https://en.wikipedia.org/wiki/RAID#WRITE-HOLE

If you then bring up battery backups, now you’re adding cost to the system.  And then some ~3-5 years later, downtime to swap the battery, and more downtime.  And all of that just to work around the RAID write hole.

Copy-on-write filesystems like ZFS and btrfs avoid the write hole entirely, so that the system can crash at any point, and the filesystem is always consistent.