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SSD's / the need for speed

Last response: in Storage
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June 13, 2007 2:40:08 AM

Hi Everyone,

Wondering if anyone had any opinions on the HDD setup im planning for a server shortly.

Server runs a relatively intensive web application for an office - running freebsd / postgresql / apache / php ... doesnt require much HDD space ... 8gb total would be ample space.

So im looking for absolute speed, not capacity. I've seen these SSD modules around and am wondering whats better? 4 x 2Gb PATA flash hdds stripped (raid 0) or (more traditional) 2 x 36Gb 15k SAS hdds stripped (ignore data redundancy for this example).

I've seen these:
http://ec.transcendusa.com/product/ItemDetail.asp?ItemI...
for $51 each and have 2 million+ erase cycles which sounds nice ... but will it be fast enough??

Alternatively there are these:
http://www.amazon.com/SanDisk-Extreme-CompactFlash-Card...
for $64 which are meant to be quite fast (40MB/sec read?) coupled with a $2 IDE adapter off ebay ... but no mention of the number of erase cycles??

Anyway, I'd be interested to hear anyones opinion on the idea ... or people that have tried this already?

Thanks in advance!
Dave.

More about : ssd speed

June 21, 2007 3:36:20 PM

Heres a peek at the CF drives over at NEWEGG

Unfortunately, I also have a question about these in terms of MTBF. If its only 1,000,000 hrs, then a 4gb card 266x has a lifespan of 6+ years. consider that, also. The true SSD's have larger capacity and double the MTBF rating. Consider 32Gb at 300x (rated for UDMA4). These are rated for about 45 years. And this is a bit misleading, as the real quotient is dependent upon MTBF and transfer rate. SOOOO... speed is not as important as the MTBF, if the manufacturer is weaselling the MTBF be careful. When in doubt, get a higher capacity than needed (this is what they want! as it artificially extends the life of the product.)

Lets also look at how I got the 6 1/3 years of life.

Lets say you have a 4gb 266x drive. At that transfer rate (266 times 150,000= 40Mb/s) It won't take long to fill a small SSD. 4Gb / (40Mb/sec) results in 100 seconds to fill the drive... or erase it! 2 million cycles (generally only the ERASURES count, as thats where the rub is for NAND flash) therefore is 200 million seconds of product life. If we divide by (60*60*24*365.25) we get the product life in years solving as 6.33+

Since the Write speed as 40Mb/sec is optomistic, we can say 'its a minimum' lifespan: at 33.3Mb/sec our lifespan increases to over 7 1/2 years.

Naturally, as one increases the SSD size, Lifespan AT THIS TRANSFER RATE, also increases.

Personally, if going with inexpensive CF drives that can do PIO4 or UDMA4, look at the amount of memory your operating system consumes, and DOUBLE IT. Thats your best bet, but not the cheapest solution.

W98se=2Gb: use 4Gb CF
XP32=4Gb: use 8Gb CF
XP64=8Gb: use 16Gb CF
V32=16Gb: use 32Gb CF

f61
!