Re: [gentoo-user] Seagate hard drives with dual actuators.

[Michael <confabulate@kintzios.com>]

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On Thursday 14 November 2024 17:00:07 GMT Dale wrote:
> Michael wrote:
> > On Wednesday 13 November 2024 23:10:10 GMT Dale wrote:
> >> Howdy,
> >> 
> >> One of my PVs is about 83% full.  Time to add more space, soon anyway.
> >> I try not to go past 90%.  Anyway, I was looking at hard drives and
> >> noticed something new.  I think I saw one a while back but didn't look
> >> into it at the time.  I'm looking at 18TB drives, right now.  Some new
> >> Seagate drives have dual actuators.  Basically, they have two sets of
> >> heads.  In theory, if circumstances are right, it could read data twice
> >> as fast.  Of course, most of the time that won't be the case but it can
> >> happen often enough to make it get data a little faster.  Even a 25% or
> >> 30% increase gives Seagate something to brag about.  Another sales tool.
> >> 
> >>  Some heavy data users wouldn't mind either.
> >> 
> >> My question is this.  Given they cost about $20 more, from what I've
> >> found anyway, is it worth it?  Is there a downside to this new set of
> >> heads being added?  I'm thinking a higher failure rate, more risk to
> >> data or something like that.  I think this is a fairly new thing, last
> >> couple years or so maybe.  We all know how some new things don't work
> >> out.
> >> 
> >> Just looking for thoughts and opinions, facts if someone has some.
> >> Failure rate compared to single actuator drives if there is such data.
> >> My searched didn't help me find anything useful.
> >> 
> >> Thanks.
> >> 
> >> Dale
> >> 
> >> :-)  :-)
> > 
> > I don't know much about these drives beyond what the OEM claims.  From
> > what I read, I can surmise the following hypotheses:
> > 
> > These drives draw more power from your PSU and although they are filled
> > with helium to mitigate against higher power/heat, they will require
> > better cooling at the margin than a conventional drive.
> > 
> > Your system will use dev-libs/libaio to read the whole disk as a single
> > SATA drive (a SAS port will read it as two separate LUNs).  The first 50%
> > of LBAs will be accessed by the first head and the last 50% by the other
> > head.  So far, so good.
> > 
> > Theoretically, I suspect this creates a higher probability of failure.  In
> > the hypothetical scenario of a large sequential write where both heads
> > are writing data of a single file, then both heads must succeed in their
> > write operation. The cumulative probability of success of head A + head B
> > is calculated as P(A⋂B).  As an example, if say the probability of a
> > successful write of each head is 80%, the cumulative probability of both
> > heads succeeding is only 64%:
> > 
> > 0.8 * 0.8 = 0.64
> > 
> > As long as I didn't make any glaring errors, this simplistic thought
> > experiment assumes all else being equal with a conventional single head
> > drive, but it never is.  The reliability of a conventional non-helium
> > filled drive may be lower to start with.  Seagate claim their Exos 2
> > reliability is comparable to other enterprise-grade hard drives, but I
> > don't have any real world experience to share here.  I expect by the time
> > enough reliability statistics are available, the OEMs would have moved on
> > to different drive technologies.
> > 
> > When considering buying this drive you could look at the market segment
> > needs and use cases Seagate/WD could have tried to address by developing
> > and marketing this technology.  These drives are for cloud storage
> > implementations, where higher IOPS, data density and speed of read/write
> > is
> > desired, while everything is RAID'ed and backed up.  The trade off is
> > power
> > usage and heat.
> > 
> > Personally, I tend to buy n-1 versions of storage solutions, for the
> > following reasons:
> > 
> > 1. Price per GB is cheaper.
> > 2. Any bad news and rumours about novel failing technologies or unsuitable
> > implementations (e.g. unmarked SMRs being used in NAS) tend to spread far
> > and wide over time.
> > 3. High volume sellers start offering discounts for older models.
> > 
> > However, I don't have a need to store the amount of data you do.  Most of
> > my drives stay empty.  Here's a 4TB spinning disk with 3 OS and 9
> > partitions:
> > 
> > ~ # gdisk -l /dev/sda | grep TiB
> > Disk /dev/sda: 7814037168 sectors, 3.6 TiB
> > Total free space is 6986885052 sectors (3.3 TiB)
> > 
> > HTH
> 
> Sounds like my system may not can even handle one of these.  I'm not
> sure my SATA ports support that stuff.

I think your PC would handle these fine.


> It sounds like this is not something I really need anyway.

Well, this is more to the point.  ;-)
 

> After all, I'm already spanning my data
> over three drives.  I'm sure some data is coming from each drive.  No
> way to really know for sure but makes sense. 
> 
> Do you have a link or something to a place that explains what parts of
> the Seagate model number means?  I know ST is for Seagate.  The size is
> next.  After that, everything I find is old and outdated.  I looked on
> the Seagate website to but had no luck.  I figure someone made one,
> somewhere.  A link would be fine.

This document is from 2011, I don't know if they changed their nomenclature 
since then.

https://www.seagate.com/files/staticfiles/docs/pdf/marketing/st-model-number-cheat-sheet-sc504-1-1102us.pdf


> Thanks.
> 
> Dale
> 
> :-)  :-) 

The only Seagate 7200RPM disk I have started playing up a month ago.  I now 
have to replace it.  :-(

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