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Havin_it
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PostPosted: Wed Sep 04, 2013 1:35 pm    Post subject: What to do with an old SSD? Reply with quote

Hi,

This is a bit of a vague question I'm afraid, but I'm totally rudderless on this one and would welcome any inspirational suggestions :D

When my old netbook died, I found myself with an oldish, low-spec SSD (Kingston V+ 100 96GB SATA2) without a home. I've hooked it up to my home server using an eSATA enclosure (necessary to retrieve its contents) but I can't think what to actually use it for.

The only benchmark of its performance I've really tried is hdparm -Tt and some simple timed writes using dd. Set against the server's main storage (ext4 on a 3-drive RAID5 array on WD Scorpio Blue HDDs), it reads only a slight bit faster, but writes up to twice as fast (with the buffer bumped up a bit).

I'm just not sure whether performance like this makes it much use as any sort of cache device (the only use that came to mind so far) but I'm also not sure how representative those crude benchmarks were, so any suggestions on useful methodology would also be welcome (can be specific to the uses you suggest). I've had a quick look at iozone and run it in both devices, but the results are pretty impenetrable to me :(

I have an ext4 partition (the netbook's old root partition) on the drive, plus some unused space. All of that is disposable now, soo I'm happy to rejig things for the sake of trying stuff out if required.

Thanks in advance?
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amospalla
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PostPosted: Wed Sep 04, 2013 1:56 pm    Post subject: Reply with quote

That old ssd has incomparable faster access time than your raid5, the real change that came with ssd storage is not it's maximum speed, but it's access time: put on it things you use daily, specially things you load a lot and or have lots of random disk access, like root, usr, portage, home (not including static content), etc ....

Another option is to use as cache, using some of the new technologies on linux (I can think of bcache) to accelerate your bigger raid5.

I hope you get the idea.
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NeddySeagoon
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PostPosted: Wed Sep 04, 2013 7:18 pm    Post subject: Reply with quote

Havin_it,

The read difference between SSD and rotating rust is latency. The SSD has almost zero latency. HDD have to seek to the track where you data is, then on average, wait half a revolution of the platter for your data to come under the read head. The latency is all dead time for data transfers.
True, the HDD and the OS both try to guess what you want to read next, so the data is cached in anticipation.

SSDs card read as fast as the memory chips allow. Higher speeds are achiever by reading more memory chips in parallel. The spinning HDD reads bits sequentially from the platter.

I'm with amospalla on how to use it.
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Havin_it
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PostPosted: Tue Sep 10, 2013 1:54 pm    Post subject: Reply with quote

Thanks both for the replies (and sorry I've left this unanswered for a while)

bcache sounds like maybe the best use (being sort of an across-the-board improvement) but I guess I'll need to swot up on it a bit.

A couple of other possibilities occurred:

* Swap space
* External journals for the Ext4 partitions
* Data partition for dirs where lots of file reading happens rapidly ($PORTAGE_TMPDIR springs to mind)

Most of these don't require that much space though; would it be unwise/counterproductive to use it for more than one of these things?
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Simba7
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PostPosted: Tue Sep 10, 2013 2:03 pm    Post subject: Reply with quote

If you're using ZFS, you can use it as an L2ARC cache.
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amospalla
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PostPosted: Tue Sep 10, 2013 2:12 pm    Post subject: Reply with quote

I suggest you moving your entire system to that ssd, but keeping on the mechanical disks big files like multimedia (image, audio and videos), first because they are big, and second because those are not being constantly accessed and/or used, and for example, listening to music or viewing a video does not benefit at all from being on a ssd.

This way, the computer will be blazing fast from boot, to day to day load and use of programs.

Even with a standard use of your computer, it is easy that you don't get to fill the ssd.
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Havin_it
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PostPosted: Fri Sep 13, 2013 4:35 pm    Post subject: Reply with quote

amospalla wrote:
I suggest you moving your entire system to that ssd, but keeping on the mechanical disks big files like multimedia (image, audio and videos), first because they are big, and second because those are not being constantly accessed and/or used, and for example, listening to music or viewing a video does not benefit at all from being on a ssd.

This way, the computer will be blazing fast from boot, to day to day load and use of programs.

Even with a standard use of your computer, it is easy that you don't get to fill the ssd.


Interesting idea, but not sure if it's so applicable for a server, where most of the system and application file loading happens at boot and not much after (I do run a couple of apps over VNC, but those usually stay running long-term as well).

As for filling up disk, that's never a challenge for a media junkie like me: hell, ripping all my CDs to FLAC ate up half of it - I'd like to do my DVDs too but I haven't enough disk for that even with the extra 96GB!

I do kinda like the idea of having the OS away from the main storage space, but if I was going to do that I'd probably just bung in a thumbdrive; just big enough (8GB should do it if you leave out $PORTDIR, /var and other cache stuff), simpler to swap out (just keep another thumbdrive with a cloned image of the first). Wish I'd done that from the get-go, now I think about it :/

I'm thinking a few GB (10?) for bcache on my homedir (this is LUKS over raid5), then the rest a data partition for $PORTDIR and maybe /var and such.

Would there be any likely issues with using it for both these things?
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