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Re: Hardware for a back up server? [WAS Re: How to use dmsetuup?]

On 11/12/23 05:15, Andy Smith wrote:

On Sat, Nov 11, 2023 at 04:01:47PM -0800, David Christensen wrote:

SSD RAID10 is very impressive when everything else matches.  Backups over a
Gigabit LAN onto SATA III SSD RAID10 does not make sense because Gigabit
Ethernet is rated for 1 Gbps read/ write and a SATA III SSD RAID10 is rated
for 24 Gbps read and 12 Gbps write.  I would put HDD's in the backup server
and put the SSD's in the workstation.


I agree with you when it comes to systems that are used purely for
backups in a style that mimics tape backup, i.e. rare need for
random access, which from what I understand does cover Gene's
situation as Gene is used to using Amanda for backups, which is a
(virtual) tape paradigm.

However, especially in a home setting, people often ask more of "the
server", turning it into something that isn't entirely, or even
primarily, a backup server. If those uses involve random access, SSD
of some kind will be very beneficial.

Also there are quite a few backup technologies that do use random
access a lot. A venerable one often mentioned on this list is
rsnapshot or its basic implementation using rsync. This walks the
entire backup tree at every iteration checking metadata and creating
hardlinks. The period of time spent deciding what to back up and how
often massively exceeds the time spent transferring and writing the
data with these systems. They will also massively benefit from low
latency storage on SSD.

So just as a word of caution -- and I know you know this, David -- I
want to say check how much random access is going on, before
deciding rotational media will cut it.
I think we agree that HDD's are slower for many (most?) backup/ restore use-cases. But, I think the slowness is acceptable for the off-hours, once a day backup use-case and for the infrequent file restore use-case that I anticipate Gene will perform. 



PS I stated this before and I have to say it again though: while
    building a dedicated backup system seems like a great idea for
    Gene's use case, the practical situation for Gene is that he's
    been trying for literal years now to make a very simple RAID10
    mdadm work on perfectly serviceable hardware. This should be a
    simple task, but it's not gone well for him and this list is
    unable to get to the bottom of why (I include myself in that, but
    I think it reflects more on communications difficulties than a
shortcoming of Linux mdadm).
There appears to be consensus to set up one storage device with one partition and one ext4 file system, and test the various applications for file access issues. It is up to Gene to decide if, what, where, when, and how. 



    I am at a loss as to why, given
    those facts, people are still advising Gene to build an entire
    new system out of parts. It makes sense for the use case but not
    for the user. I don't think it's supportable. For this user I
    would have to still stand by my advice of buying an off-the-shelf
    NAS.



I think we agree that everyone needs backups.
It is my impression that most of Gene's eggs are in one basket (the computer with the Asus Prime Z370 A II motherboard) and that Amanda has been broken for a while (?). I would celebrate Gene implementing working backups by any means on any device and any media. Again, Gene decides. 


David
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