On Wed, 12 Jul 2023 20:44:08 -0400
Steve Litt <slitt@???> wrote:

> Simon said on Wed, 12 Jul 2023 18:22:14 +0100
>
> >Steve Litt <slitt@???> wrote:
> >
> >> You just reminded me why I don't use RAID.
> >
> >I find that statement interesting. What do you use instead - rely on
> >backups ?
>
> Anyone who doesn't rely on backups, whether they have RAID or not, is
> cruisin for a bruisin. RAID is no substitute for a backup.

Yes of course, best if off site, you need them if your shop
burns down or your is hit by a lightning.

> >
> >
> >md on Linux is actually quite easy to use.
>
> Your eight step procedure didn't look easy.
>
> [snip]
>
> >I’ll add that my viewpoint is coloured by having had my backside saved
> >by raid so many times. Yes, if a disk fails you can replace it,
> >restore your backups, and carry on.
>
> No doubt that restoring everything from backup including system files
> (which I don't back up) is a PITA. But all these layers of abstraction
> heaped on top of the simplicity of EXT4 make a mistake during repair a
> lot more likely.

Isn't it the other way the simplicity of EXT4 is sitting on top of
a fully transparent (to EXT4) layer of md abstraction?

> > But in a business world
>
> s/business world/big business world/
>
> >that takes
> >on a whole new meaning : Firstly, there WILL be lost data, typically
> >everything all your staff did today since last night’s backup.
> >Secondly, you’ll have people sat around twiddling their thumbs while
> >to get everything back up again - just the restore typically takes
> >“hours”. In business,
>
> Big business
>
> >there really is no case for not using raid on
> >anything but things like mass desktops/laptops that can be rebuilt
> >easily and which don’t hold any data.
>
> For big business, this is absolutely true. The business has the money
> for all the extra disks, and they have the money to hire and/or train
> talent proficient in RAID and LVM. With lots of users, and with quick
> customer response on the line, there's no alternative.

Extra Disks, the minimum you need for redundancy of data is 2 disks
so extra costs are not that high, plus maybe a spare disk you keep
for fast replacement (shared between a few boxes).

> >
> >And at home, I have raid on my Linux boxes. I just don’t want the
> >hassle, lost time, and lost data from having to restore (e.g.) my mail
> >server (or rather, the host it’s a VM on) from a backup if a disk
> >fails. And I have had disk failures, but I’ve been able to replace
> >them and do a hot rebuild without any downtime or lost data. That’s
> >been well worth the extra cost of hardware, and the time taken to set
> >it up.
>
> IIRC it's been over a decade since I had a disk failure on my Daily
> Driver Desktop (ddd). I replace my ddd every 5 years, and usually buy
> all new, high quality Western Digital or other high quality disks. No
> seagate ever touches my equipment. But of course, I'm a one man band.

You are a lucky man, I had disk failures at home and work and raid
always saved my ass, especially at work it avoided downtime and thus
loss of revenue.
I would also not buy batches of new disks for a raid array all of the same
model and brand but rather mix different brands to avoid a faulty
or problematic batch having disks failing at the same time making
recovery difficult or impossible.

> >That’s not to say I don’t have backups as well, raid only protects you
> >agains a failed disk - not again other mishaps such as “oops, that
> >wasn’t the directory I intended to delete”.
>
> Yes!
>
> >Of course, the operations I and others have suggested have come about
> >from a desire to repartition disks into different arrays. That’s not a
> >common requirement - and again, the fact that with md it’s possible to
> >do so while keeping your data on the internal disks is almost magical
> >compared the other raids I’ve previously used where the ONLY option
> >would be to nuke the array and your data before building new ones.
> >
> >And a way to avoid the requirement the OP asked for is, as I do, to
> >add LVM on top of the array - though I think LVM can handle the raid
> >as well now ? So two levels of abstraction between partitions on disk
> >and filesystems - I would say in the Linux world we are blessed with
> >this richness of capabilities.
> >
> >And I confess I keep thinking I should have a proper look at ZFS - but
> >I just never find the time, and I already know md + lvm “well enough”
> >for my now fairly modest needs.
>
> I consider ZFS from time to time.

I use it on the same nas box: one ext4 raid array exposed as samba share
for the other win clients to backup and a zfs on separate disks not exposed to
the network to copy over the very important stuff and have snapshots so that
previous copies of backups could be restored if needed.

Ciao,
Tito
>
> SteveT
>
> Steve Litt
> Autumn 2022 featured book: Thriving in Tough Times
> http://www.troubleshooters.com/bookstore/thrive.htm
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