[chbot] Urgent help with disk partitioning

[Robin Gilks]

Thanks for all the ideas and hints. It's rebuilt now.

Mostly an issue of not remembering how I built it 10 years ago but also
that the ST3000DM001 is no longer available and the ST3000DM008 replacement
has a small number of sectors (by a very small margin) so as soon as a
partition takes some of them the disk is too small to add to the array.

I'll be asking questions about the wifes iMac in due course - after an OS
update some of the apps don't appear in the App Store to be updated even
though there are much later versions!



On Thu, Jul 20, 2023 at 5:30 PM Volker Kuhlmann <list57 at top.geek.nz> wrote:

> On Thu 20 Jul 2023 10:37:52 NZST +1200, Robin Gilks wrote:
>
> > I'm replacing a failed disk in my raid array
>
> General reply.
>
> I avoid GUI disk partition stuff because I don't trust it telling
> me exactly what's going on. I never had a use for parted.
>
> There was a time when fdisk couldn't handle GPTs and gdisk was needed.
> fdisk has now acquired that functionality so that's all you need.
>
> When you create disk partitions and raid arrays make some careful notes
> about the parititon boundaries and array configuration, should you ever
> be in your present situation... It amounts to redirecting output of some
> programs (fdisk -l, mdadm with different options) to files. Remember on
> Linux you can always recover damaged partition tables and not lose the
> filesystem, *if* you know the block numbers. Any partitioning tool also
> creating filesystems unless explicitly told (fdisk, gdisk, sfdisk etc
> aren't able to) needs to be deleted now.
>
> Do yourself a favour and make separate arrays for system, home, and
> data. Or at least for system.
>
> Depending on your disks, it might be useful to know that constituent
> partitions do not need to start at the same block numbers. Mirror sda2
> with sdc6 if it suits.
>
> All assuming Linux softraid. I wouldn't consider anything else, unless
> it's a proper hardware-raid controller card. I think they're $k.
> Anything around $100 (used to be common) makes you worse off, it's
> propriatary rubbish for no performance gain. Card dies, buy exact same
> model or data gone. That stuff is integrated in better mobos these days,
> waste of silicon. Dead mobo, dead data.
>
> Be careful with consumer disks in RAID arrays. There are plenty of
> warnings online, relating to response times being taken as dead disk,
> and random read errors (likely with today's TB disks) taking the disk
> out of the array and combined with other factors creating a
> non-recoverable situation (data gone).
>
> I ignored that, so far, so mostly good. For the past 4 years I've used
> ST4000DM004, WD40EZRZ, and a top-end SSD (Samsung 970 Evo Plus) in
> RAID1. It worked perfectly until an OS upgrade late last year, and it
> took me months to find out why something in the system was going like
> treacle (e.g. 1-2s delay for less to exit in a terminal). The problem
> disappeared once I took the ST4000DM004 out of the array (its SMART
> status is perfect) so I see Seagate STx000DM as useless for arrays. The
> nuisance is that better disks are noisier.
>
> Never use disks from the same batch in a RAID array... and ST2000DM were
> rubbish and dies around warranty time.
>
> Back to your problem, DOS partition tables are good for 2^32 block or
> 2TB disks. Larger requires GPT, which creates some dummy DOS table to
> fool tools into thinking there is a table present (there is, it's just
> GPT, but the old tools don't get that).
>
> If you have an old Linux and your fdisk doesn't do GPT, use gdisk. It
> works basically like fdisk. To add a clean disk to your array, create
> partitions of the same size as the others in the array. Remember that
> the partition is a few kb larger than the filesystem - RAID superblock,
> and there are options for its location. Your mdadm will take care of
> that. Create the partition layout, mark the partition as raid type
> (potentially optional), make the kernel reload the disk table after
> change (or reboot), and use mdadm to add the empty/unformatted
> partitions to the array.
>
> Check rebuild status etc with cat /proc/mdstat
>
> Bonus for doing all that with LVM and encrypted disks and partitions in the
> mix...
>
> Volker
>
> --
> Volker Kuhlmann
> http://volker.top.geek.nz/      Please do not CC list postings to me.
>
> _______________________________________________
> Chchrobotics mailing list Chchrobotics at lists.ourshack.com
> https://lists.ourshack.com/mailman/listinfo/chchrobotics
> Mail Archives: http://lists.ourshack.com/pipermail/chchrobotics/
> Meetings usually 3rd Monday each month. See http://kiwibots.org for
> venue, directions and dates.
> When replying, please edit your Subject line to reflect new subjects.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ourshack.com/pipermail/chchrobotics/attachments/20230720/1daa9318/attachment.html>