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#1 2008-06-06 13:00:41

dhave
Arch Linux f@h Team Member
From: Outside the matrix.
Registered: 2005-05-15
Posts: 1,112

Can I put /tmp on an SD card?

My new laptop has a built-in flash card reader, and I have a spare 1Gb SD card. I'm wondering if it would be good to mount /tmp on the SD card. I have a few questions first:

(1) Is this possible? I wasn't sure whether the SD card would be recognized soon enough in the boot sequence.

(2) Would there likely be a speed advantage?

(3) What should my fstab entry look like? The SD card is designated as /dev/mmcblk0p1 with a vfat filesystem.

(4) Is there something other than /tmp that I should mount there?

Thanks very much.


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#2 2008-06-06 13:23:33

Morra
Member
Registered: 2008-05-16
Posts: 39

Re: Can I put /tmp on an SD card?

Why are you interested in doing this? Usually people want to use RAM with temp folder. The transfer rate of SD cards are often below 20 Mb/s. Hard drive speeds are measured in gigabytes. For performance you should definately use hard drive.

If you want to try mounting your card at boot you can check out the wiki: http://wiki.archlinux.org/index.php/Fstab It will explain how to edit Fstab.

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#3 2008-06-06 13:29:29

dhave
Arch Linux f@h Team Member
From: Outside the matrix.
Registered: 2005-05-15
Posts: 1,112

Re: Can I put /tmp on an SD card?

Morra wrote:

Why are you interested in doing this? Usually people want to use RAM with temp folder. The transfer rate of SD cards are often below 20 Mb/s. Hard drive speeds are measured in gigabytes. For performance you should definately use hard drive.

If you want to try mounting your card at boot you can check out the wiki: http://wiki.archlinux.org/index.php/Fstab It will explain how to edit Fstab.

I naively assumed that because the SD card is solid state, it would be much faster than my hard drive. If not, then of course I'm not interested. Speed was my motivation, Morra, speed, speed, speed.


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#4 2008-06-06 15:02:29

sirocco
Member
Registered: 2008-03-10
Posts: 149

Re: Can I put /tmp on an SD card?

Morra wrote:

Hard drive speeds are measured in gigabytes.

Few gigabites. Really ~50MB/s and less for 2.5" HDD. And high seek time.

Another limitation is that flash memory has a finite number of erase-write cycles

http://en.wikipedia.org/wiki/Flash_memory

Last edited by sirocco (2008-06-06 15:08:19)

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#5 2008-06-06 15:09:36

.:B:.
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Registered: 2006-11-26
Posts: 5,819
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Re: Can I put /tmp on an SD card?

Morra wrote:

Hard drive speeds are measured in gigabytes.

If you have evidence to back that up I'd be most happy to see it.


Sirocco: Not gigabites, gigabit wink. And HD transfer speeds up till now are still megabit (Mb), some high-end SSDs are said to get a gigabit, but I haven't seen any benches yet.

'Solid state' is no magic word, the new SSDs may make it look like that, but only the high-end versions rival regular HDDs performance-wise. Take the 'SSD' for example that MSI or Asus put in their UMPCs, they will barely match the performance of a regular HDD. And there is not a single flash card (MemoryStick, xD, SD, SDHC, ...) that comes close to a normal HD's performance.

If you want  to do something fancy with your /tmp, put it in RAM. Provided you have enough.

Last edited by B (2008-06-06 15:11:20)


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#6 2008-06-06 15:53:55

lilsirecho
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Registered: 2003-10-24
Posts: 5,000

Re: Can I put /tmp on an SD card?

Perhaps the use of Compact Flash cards with "true Ide" format will provide a respectable 45MB/sec read/write speed..at least they do well in my system ,FaunOS.


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#7 2008-06-06 16:38:57

dhave
Arch Linux f@h Team Member
From: Outside the matrix.
Registered: 2005-05-15
Posts: 1,112

Re: Can I put /tmp on an SD card?

B wrote:

'Solid state' is no magic word, the new SSDs may make it look like that, but only the high-end versions rival regular HDDs performance-wise. Take the 'SSD' for example that MSI or Asus put in their UMPCs, they will barely match the performance of a regular HDD. And there is not a single flash card (MemoryStick, xD, SD, SDHC, ...) that comes close to a normal HD's performance.

That's interesting. I would have thought that something with moving parts would be necessarily slower than something with no moving parts, if only because of the loss of energy due to friction. I base this on my extensive study of this topic in Mrs. Casey's 7th grade physical science class in 1968. roll


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#8 2008-06-06 18:07:22

Morra
Member
Registered: 2008-05-16
Posts: 39

Re: Can I put /tmp on an SD card?

B wrote:

If you have evidence to back that up I'd be most happy to see it.

No, I don't have any evidence roll
I just remembered that my hard drive had a label that said 1.5 Gbits (not bytes). That obviously isn't the right speed as mentioned above.

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