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I need to hugely extend RAM in the platform I can't do it. As a temporary solution I want to use swap for it. What is better to use for swap storage - an SSD or 15k HDD like Cheetah? I understand that anyway it'll be slower than RAM.

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migrated from serverfault.com Dec 12 '11 at 5:58

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3 Answers 3

up vote 3 down vote accepted

disclaimer: i've never tried it.

gut feeling tells me ssd will do a better job and ... will die much sooner in the process - it offers much higher number of i/o's per second than physical hard drive [even if it's 15k rpm it's still 250 seeks/sec vs thousand or more]. but... hard drive will have much smaller addressable block - probably 512B, while ssd will have to erase 16-64kB even if single bit is changed in the swapped page.

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Your gut feeling is right. It has higher IO bandwidth and a TON more IOPS so it is better. That said ;) It sucks still - more ram is the better solution. –  TomTom Dec 10 '11 at 17:46
    
He, you're completely right! My MacBook Pro loves using ~6GBs of swap (I have 8GBs of RAM already in here) on my SSD and things work much smoother than if I tried to do that on a hard drive. Or if the OP has the money, I'd put two SSDs in RAID and it'll scream. :P –  Taylor Jasko Dec 10 '11 at 18:10
    
"will die much sooner in the process" - This is no longer true of SSDs. Any modern one should outlast HDDs if they work at all - due to wear-levelling. –  thomasrutter Dec 12 '11 at 6:12
    
No, wear-levelling is unrelated to TRIM and doesn't require any support from the OS or controller. It's implemented by the SSD. It cannot be disabled as it is fundamental to how the drive operates on a low level. Any brand-name SSD bought in the last 3 years will do it internally. –  thomasrutter Dec 13 '11 at 0:35

How about a SATA RAM disk? If SATA is too slow, how about PCI-E?

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The SSD will do a better job than a single 15k disk. Can you provide some numbers, though? Have you already exhausted the swap on your system?

If the need to extend RAM on the platform is important enough for you to care about SWAP performance, then it's probably important enough to obtain the right amount of RAM.

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I'm not able to increase RAM due to motherboard limiations (it's a desktop and I already installed 16GB) and using swap brings at least ~100 (or more) GB of extra memory. –  flashnik Dec 10 '11 at 17:46
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Before you paint yourself in the corner, you need to prioritize obtaining a server class board - it'll be worth it versus having a scratch disk for swapping ... –  thinice Dec 10 '11 at 17:59

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