swap_pager indefinite wait buffer - question - SOLVED

[PeerCorps Trust Fund]

Hi!

Thanks for the below. This is all extremely helpful and I agree with it entirely.

The main limitation in this case, for now at least, is that we are mainly dependent on donated computer equipment from individual donors. We try to use everything as much as possible (hence the constant search for an OS that can make the most of slightly older equipment). 

We might get a Thinkpad x200 for example (which comes with a 250 Gb HD or so), and have on hand around 2 terabytes of recorded secondary school lectures and e-books to load on it. In the one case mentioned previously, the internal HDD was swapped out in favor of an SSD. A WD Passport 2TB drive is connected to it. Dragonfly is installed on the SSD with half of it (50 gigabytes) being used for swap. This appears to be working, but once we get a few more workstations connected to it we will see how far we can push it! Probably the simultaneous connections will show a lag, but we are hoping that swapcache might make a difference there.

On 12/27/2014 06:33 AM, Matthew Dillon wrote:
> Ultimately the most robust storage solution is going to be a permanent,
> direct SATA-connected SSD, either 2.5" or a M.2 form factor depending on
> the hardware.  It's possible to make it very lean, the system can easily be
> installed in a small ~64GB SSD.  With a USB stick, definitely not (the
> stick will wear out very quickly).
> 
> As long as one is not writing gigabytes to the SSD every day, it will last
> forever.  Even though HDDs (spinning rust) might be cheaper, they they will
> die relatively quickly in a rough environment and require replacement (or
> the equipment will wind up just being unusable and junked when they fail).
> 
> Another advantage of a small SSD is that swap space can be configured on
> it, which means the system can page very efficiently to/from it and be able
> to make far better use of the 1GB of ram.  And with a SSD, paging from swap
> is very fast so users won't notice the lag as much if running a big program.
> 
> USB-attached hard drives are not going to be as reliable as direct SATA
> connected drives for several reasons, the main one being that the system
> can't survive a disconnect/reconnect if root happens to be on the
> usb-connected drive.  Performance is also going to suffer significantly
> with USB-attached drives verses direct SATA-attached drives.  SATA attached
> drives will use the AHCI driver and can handle high concurrent loads even
> in lean configurations (paging to/from swap can create high concurrent
> loads).
> 
> -Matt
> 
> On Fri, Dec 26, 2014 at 8:12 PM, Matthew Dillon <dillon at backplane.com>
> wrote:
> 
>> That's an excellent use of a free OS.  I was in Tanzania at the beginning
>> of the year on vacation.  You can do a lot with 1GB and a lean UI.  All the
>> BSDs should do quite well in that configuration.
>>
>> -Matt
>>
>> On Fri, Dec 26, 2014 at 4:05 AM, PeerCorps Trust Fund <
>> ipc at peercorpstrust.org> wrote:
>>
>>> It certainly is, although the machines are actually running stock FreeBSD
>>> 10.1.
>>>
>>> PC-BSD was an option in the beginning, but because these were older
>>> computers it was easier to build a low-resource install enabling only basic
>>> services such as NFS rather than trying to pare down a PC-BSD install to
>>> suit the needs of the project (which is a basic KDE-based workstation).
>>>
>>> Most of those desktops had only one gigabyte of RAM ad PC-BSD uses a lot
>>> of resources. We learned a lot in the process and will be implementing
>>> modified libraries in the coming year using donated computer equipment.
>>>
>>> I think many underestimate the enormous value that such projects have in
>>> these communities. Just having access to books and educational material is
>>> tremendously beneficial from a development perspective.
>>>
>>> On 12/26/2014 01:12 PM, Carsten Mattner wrote:
>>>> On Fri, Dec 26, 2014 at 12:43 AM, PeerCorps Trust Fund
>>>> <ipc at peercorpstrust.org> wrote:
>>>>> Indeed in Tanzania :) we have a couple of technology initiatives
>>> taking place at the
>>>>> moment and *BSD is at the center in many ways. The delivery of
>>> educational
>>>>> materials and books to resource-limited communities is an important
>>> aim of
>>>>> these initiatives.
>>>>>
>>>>> We actually used FreeBSD in our first effort, but want to experiment
>>> with some
>>>>> of the capabilities of DragonflyBSD and HAMMER in the next one. In our
>>>>> estimation we can possibly stretch our hardware and funds a bit
>>> further with
>>>>> DragonflyBSD/HAMMER owing to its low resource requirements.
>>>>
>>>> Ah nice. Is it the same project we heard recently of with photos of a
>>> library
>>>> room running PCBSD machines with a video and document library?
>>>>
>>>>
>>>>> On 12/25/2014 11:20 PM, Carsten Mattner wrote:
>>>>>> On Thu, Dec 25, 2014 at 7:08 PM, PeerCorps Trust Fund
>>>>>> <ipc at peercorpstrust.org> wrote:
>>>>>>> I just wanted to take the opportunity update a previous post that I
>>> made to the
>>>>>>> list concerning a swap_pager concern. It isn't an issue at all but
>>> the fault of my
>>>>>>> own ignorance and hardware limits.
>>>>>>>
>>>>>>> The external drive in question was simply not pulling enough power
>>> from the
>>>>>>> USB port of the laptop. This was likely resulting in a stalled drive
>>> when anything
>>>>>>> substantial was being copied to it.
>>>>>>>
>>>>>>> This has since been solved by connecting the drive first to an
>>> externally powered
>>>>>>> USB hub. So, if there is anyone else out there having a similar
>>> issue, trying this
>>>>>>> seems to do the trick. Alternatively, just use a drive that is
>>> powered externally.
>>>>>>>
>>>>>>> Everything works beautifully now and this low cost experiment for a
>>> simple file
>>>>>>> server will find a home in a school classroom next year.
>>>>>>
>>>>>> In Tanzania?
>>>>>>
>>>>>> FreeBSD had a writeup about a set of PCBSD machines installed in
>>> Nigeria IIRC.
>>>>>>
>>>>>> A blog post or other writeup to link on dragonflybsd.org would
>>> surely be nice.
>>>>>>
>>>>>
>>>
>>> --
>>> Michael L. Wilson
>>> International Project Coordinator
>>> PeerCorps Trust Fund - Tanzania
>>>
>>>
>>>
>>
> 

-- 
Michael L. Wilson
International Project Coordinator
PeerCorps Trust Fund - Tanzania