Re: [gentoo-user] External hard drive and idle activity

[Mick]

On Monday, 6 January 2020 08:48:13 GMT Stefan Schmiedl wrote:
> Dale,
>
> "Dale" <rdalek1967@×××××.com>, 06.01.2020, 09:29:
> > Also, when looking for a drive to buy, what should one look at to see if
> > it is a SMR drive?

You will need to visit the OEMs website and dig into the documentation they 
provide.  Keywords like "archive drive/disk/format", "shingled magnetic 
recording" and "SMR", would be a giveaway this is not a normal PC drive.


> > While it may be OK for my backups, I'd like to avoid
> > them on the drives inside my rig that are used for the OS or /home.  I
> > dunno, just a gut thing.
>
> it's not "just a gut thing". SMR drives are not meant for random
> access writing; they write like a tape and read like a disk.
>
> A while ago, one of my clients bought one of those things
> to replace an older failing backup drive. The next night, the
> backup took hours instead of minutes. No knowing what was inside
> the box, I did some measurements and discovered that the first
> few files were written quickly, then things got really slow,
> with the rsync process waiting (state "D") for the drive to
> finish.
>
> tar-based backups went much quicker, though, which matches the
> expected behaviour of SMR drives; the drive did not need to rewrite
> many large areas due to many small changes, instead it only had to
> write one large area due to one large change.
>
> s.

Stefan reinforced a point made earlier by Richard (I think).  These drives are 
only good for linear backups, like tar performs when it appends newer files to 
an existing tarball.  If they are used as normal PC drives for regular writing 
of data, or with back up commands which use rsync, cp, etc. then the disk will 
fail much sooner than expected because of repeated multiple areas being 
deleted, before each smaller write.  I recall reading about how short the life 
of SMR drives was shown to be when used in NAS devices - check google or 
youtube if you're interested in the specifics.

Personally, I would only use such a drive for 'keepers'.  Say, films I intend 
to write once and watch many times, ripped music albums, family photos, etc.  
For OS files and other temporary backups I would use a normal PC drive.

PS. When you put together a tar script do not forget to add --xattrs.  If not, 
you'll find some commands break when you run them from a restored fs.
-- 
Regards,
Mick