Re: Advice on system purchase
Am Freitag, 2. November 2012 schrieb lee:
> Martin Steigerwald <Martin@lichtvoll.de> writes:
> >> SSDs are a waste of money unless you do have the workload to benefit
> >> from them. And if you have that, where do you store your data?
> >
> > I disagree.
> >
> > Putting an SSD in this laptop has been the single most effective way
> > to improve all my desktop workloads like it was when I switched from
> > floppy disk to harddisk. Its just insane. This machine is to
> > frigging fast…
>
> Hm what applications or what kind of workload exactly are you talking
> about?
Anything I do on this machine.
- Starting complex applications: its just *way* faster.
- Booting.
- Compiling kernels.
- Backup via rsync
- apt-get dist-upgrade
- you name it.
Writing a mail if the application for it is already loaded? Unlikely.
But then how much CPU time is your mail program eating up? I would
be surprised if this surpasses 30% on average. Heck I would be surprised
if this surpasses 10% of one core on average.
So I type something and see how it goes. And there is no kmail above
10% CPU at all. Peak CPU. Not average. Similar goes with an office
application unlike you edit really complex documents.
> > If the CPU isn´t too slow for it and most current CPUs aren´t, a SSD
> > will be highly beneficial for just about any workload that is using
> > random I/O. And most workloads are.
>
> Like? When you edit a text in an editor or a WYSIWYG word processor or
> when you work on a spreadsheet, you are not creating a lot of disk I/O.
If the application is already loaded yes. But then my point is that
you aren´t causing much CPU either.
> When you compress or uncompress a tar archive, you are CPU limited.
That highly depends on its contents and the packing algorithm. With
mostly random files I doubt it for a usual harddisk.
I got it to 100%, but I think thats due to SSD.
martin@merkaba:~/Zeit> /usr/bin/time -v tar -xf /usr/src/linux-source-3.2.tar.bz2
Command being timed: "tar -xf /usr/src/linux-source-3.2.tar.bz2"
User time (seconds): 26.08
System time (seconds): 3.38
Percent of CPU this job got: 101%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:29.14
Average shared text size (kbytes): 0
Average unshared data size (kbytes): 0
Average stack size (kbytes): 0
Average total size (kbytes): 0
Maximum resident set size (kbytes): 3964
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 1086
Voluntary context switches: 102399
Involuntary context switches: 108885
Swaps: 0
File system inputs: 0
File system outputs: 998072
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 0
Page size (bytes): 4096
Exit status: 0
Could you send output with a usual harddisk?
martin@merkaba:~/Zeit> LANG=C df -hT .
Filesystem Type Size Used Avail Use% Mounted on
/dev/mapper/merkaba-home ext4 221G 209G 9.1G 96% /home
> When you use a web browser, you are limited by the bandwidth of your
> network connection and by CPU --- not to mention your graphics card.
Graphics, CPU? With a webbrowser? Did you ever watch top while surfing
the web?
Look at this:
merkaba:~> atopsar -O -b 18:00 -e 19:30
merkaba 3.6.0-tp520 #8 SMP PREEMPT Wed Oct 3 13:05:36 CEST 2012 x86_64 2012/11/08
-------------------------- analysis date: 2012/11/08 --------------------------
18:30:43 pid command cpu% | pid command cpu% | pid command cpu%_top3_
18:40:43 2817 kmail 7% | 1713 Xorg 4% | 2533 kwin 2%
18:50:43 1713 Xorg 5% | 2817 kmail 5% | 2533 kwin 3%
19:00:43 2627 virtuoso 20% | 2986 nepomuks 18% | 2983 nepomuks 16%
19:10:43 1713 Xorg 6% | 2817 kmail 5% | 2533 kwin 4%
(I exclude the day cause I wasn´t working much with the system.
While you may take advantage on peak performance to reduce latencies,
neither firefox nor anything on this machine does yield a significant
challenge to the CPU.
The CPU is so bored it isn´t funny anymore.
> When you play a game, you are limited by graphics card and CPU and
> perhaps by memory bandwidth. When you do photo editing in gimp,
> you're limited by CPU and perhaps memory bandwidth and your graphics
> card, and you my be limited by having to swap.
With gaming I agree.
> Loading the editor or word processor or spreadsheet, tar and bzip2, the
> web browser and the game will probably be faster unless they are
> already in the disk cache. Swapping will probably be faster as well.
>
> I just tried with a stop watch: It takes 3 seconds to start
> libreoffice, and I have slow disks. What does it matter if it takes
> only 1.5 or 2 seconds when you have an SSD instead?
Did you try this after cold boot?
> > Thus I would go rather with some dual core i5 + SSD than with a
> > quadcore i7 + harddisk. Save a few bucks on the CPU if you can
> > afford a good SSD then.
>
> I'd rather go with the quadcore.
And your current workloads is actually using how many of these four
cores?
Did watch at my powertop snapshots?
On writing this mail with two KDE sessions fully loaded and running
with two kmails, two iceweasels, lots of konsole and so on I just get:
PowerTOP v2.0 Overview Idle stats Frequency stats Device stats Tunables
Package | Core | CPU 0 CPU 1
| | C0 active 3,5% 1,2%
| | POLL 0,0% 0,0 ms 0,0% 0,0 ms
| | C1-SNB 1,3% 0,3 ms 0,5% 0,6 ms
C2 (pc2) 3,0% | |
C3 (pc3) 1,4% | C3 (cc3) 1,6% | C3-SNB 1,2% 1,3 ms 0,0% 0,0 ms
C6 (pc6) 8,5% | C6 (cc6) 0,0% | C6-SNB 0,0% 0,0 ms 0,0% 0,0 ms
C7 (pc7) 48,5% | C7 (cc7) 84,3% | C7-SNB 88,1% 3,0 ms 96,3% 5,4 ms
| Core | CPU 2 CPU 3
| | C0 active 4,6% 0,6%
| | POLL 0,0% 0,0 ms 0,0% 0,0 ms
| | C1-SNB 0,1% 0,2 ms 0,0% 0,0 ms
| |
| C3 (cc3) 0,7% | C3-SNB 0,3% 0,7 ms 0,0% 0,0 ms
| C6 (cc6) 0,1% | C6-SNB 0,1% 0,8 ms 0,0% 0,0 ms
| C7 (cc7) 85,8% | C7-SNB 89,7% 3,2 ms 98,4% 11,0 ms
PowerTOP v2.0 Overview Idle stats Frequency stats Device stats Tunables
Package | Core | CPU 0 CPU 1
| | Actual 929 MHz 909 MHz
Turbo Mode 1,7% | Turbo Mode 0,4% | Turbo Mode 0,3% 0,1%
2,50 GHz 0,0% | 2,50 GHz 0,0% | 2,50 GHz 0,0% 0,0%
2,00 GHz 0,0% | 2,00 GHz 0,0% | 2,00 GHz 0,0% 0,0%
1,80 GHz 0,0% | 1,80 GHz 0,0% | 1,80 GHz 0,0% 0,0%
1,60 GHz 0,0% | 1,60 GHz 0,0% | 1,60 GHz 0,0% 0,0%
1400 MHz 0,0% | 1400 MHz 0,0% | 1400 MHz 0,0% 0,0%
1200 MHz 0,3% | 1200 MHz 0,2% | 1200 MHz 0,1% 0,1%
1000 MHz 0,0% | 1000 MHz 0,0% | 1000 MHz 0,0% 0,0%
800 MHz 7,4% | 800 MHz 2,1% | 800 MHz 1,9% 0,3%
Idle 90,7% | Idle 97,3% | Idle 97,6% 99,5%
| Core | CPU 2 CPU 3
| | Actual 1188 MHz 839 MHz
| Turbo Mode 1,7% | Turbo Mode 1,7% 0,0%
| 2,50 GHz 0,0% | 2,50 GHz 0,0% 0,0%
| 2,00 GHz 0,0% | 2,00 GHz 0,0% 0,0%
| 1,80 GHz 0,0% | 1,80 GHz 0,0% 0,0%
| 1,60 GHz 0,0% | 1,60 GHz 0,0% 0,0%
| 1400 MHz 0,0% | 1400 MHz 0,0% 0,0%
| 1200 MHz 0,3% | 1200 MHz 0,3% 0,0%
| 1000 MHz 0,0% | 1000 MHz 0,0% 0,0%
| 800 MHz 7,4% | 800 MHz 7,4% 0,2%
| Idle 90,7% | Idle 90,7% 99,8%
So I am not using half of the MHz on average. And my Linux uses mostly
*one* core. 1,7%
*One* core. Just one.
So while I can imagine that in certain peak situations two cores may help,
I am with Stan that I highly doubt that more than two cores give you much
benefits if at all over a good dual core CPU, unless you do
make -j4
all the time.
When you have workloads that take advantage of four cores, fine, use a quadcore
CPU. With typical desktop workloads I doubt it.
> > And where to store that data? On the SSD.
>
> How much does it cost to make a 4TB RAID-5 and a 500GB RAID-1 with
> SSDs, plus having the capacity for backups? What would be the
> advantage?
As I said for certain types of files an SSD would be a price sink.
And if you are using 4 TB of space I bet that you are using those kind
of *big* files. I.e. anything above 1 MiB or so like music and video
files.
For these files you get almost sequential harddisk access if fragmentation
isn´t to high.
But for maildirs like KMail uses you are like to get some 70-100 2-16 KiB
IOPS out of it. Thats not more than about 2 MiB per second. With good
SSDs you get 4000 IOPS out of it.
So we have another usecase: KMail with local mail storage, be it POP3 or
disconnected IMAPS does a lot faster with SSD. I bet opening that
more than 30000 mail folder for linux kernel mailinglist or even just
nepomuk desktop search indexing would *crawl* on your RAID5.
> And I'm going to need some more disk space when trying out other
> distributions and maybe even windoze in the process of getting rid of
> Debian.
I do not intend to do this.
> > Anyway, in desktops and partly in laptops as well you can combine
> > them. Put random I/O data like OS, applications, mails and other
> > small files on SSD and have a harddisk for photos, music, videos and
> > so on. Thus you get the best of both worlds.
>
> For the money I'd have to pay for the SSDs, I'm better off buying 2TB
> or 3TB hard drives and just attach them to the RAID. I don't store
> data on a single disk anymore since a long time because I've seen too
> many disks failing, so keep in mind that when you talk about "a disk",
> it is always at least two of them.
>
> When my system disks fail, I'll go look on ebay and try to get
> something like two or three ~320GB disks for about EUR 25 each, or
> whatever is available in reasonable size and price. SSDs can't
> compete with that, other than being --- for every day usage
> insignificantly --- faster.
OK, so I close with a last question:
Did you ever try actually a good SSD?
Or are you talking about what you think a good SSD can do?
If you are just thinking:
Try it.
Cause if you tried it, you can see for yourself.
Heck, why do I even take the time to try to prove anything when it is
so openly visible?
In my subjective perception going from harddisk to SSD, yes I also
upped CPU and memory on that move significantly, but I heard of people
who juse replaced harddisk by SSD, was like switching from floppy disk
to harddisk.
> > Hopefully soon BTRFS will be able to use SSD as cache with the new
> > VFS hot data tracking feature and then you would not have to
> > distribute data manually between SSD and harddisk anymore.
>
> I think my RAID controller can do something like that maybe. Since
> SSDs wear out the faster the more you write to them, I'm not so sure
> what the real benefit of such a setup is unless you don't care about
> the money --- or have a workload for which it does matter.
Well I close with:
http://baarf.com
Take it or leave it.
If you are fine with your RAID 5, use it.
I wouldn´t.
Well and another one that may come handy at times:
merkaba:~> systemd-analyze
Startup finished in 3899ms (kernel) + 2695ms (userspace) = 6595ms
Granted, till display manager displays prompt takes a few seconds longer,
but you can forget anything like that on a usual harddisk.
I do not boot often, but I do often close and open applications and there
it comes handy. Well I do see some of those benefits with just using
lots of RAM. A workstation at work has 12 GB RAM and RAID-1 (not RAID-5)
and nice dual or quadcore CPU. And since I upped from 4 GB to 12 GB
I noticed somewhat that resembles SSD feeling at times. But only when
application has been loaded before already. Cause Linux VM just has it
cached.
So while an SSD + 700 MHz slow speed CPU wouldn´t make much sense, I´d
still prefer any modern dualcore desktop CPU with some power with SSD in
spite of a superduper power quadcore CPU without SSD.
If I can have a quadcore CPU + SSD, why not?
But no SSD?
No way for me. Even in a desktop I´d put one meanwhile. While storing big
files on convential harddisk.
I might go this route for this laptop as well, cause that 320 GB
Intel SSD 320 is almost full. Add a harddisk. But I will not remove
that SSD from it. Except for replacing with a bigger SATA-600
SSD :)
If you want to go another route, fine.
I think I made my point.
Thanks,
--
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA B82F 991B EAAC A599 84C7
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