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we decided to upgrade DB server, now running on FreeBSD 8.0-STABLE, Intel(R) Xeon(R) CPU E5335 @ 2.00GHz (1995.01-MHz K8-class CPU), 8GB RAM, db running on SAS hdd with slave on another box, there are more than 2000 queries per second to database, DB size is 25 GB.

I am completely new to SSD technology, I was reading a lot of information, but I am still not sure, which SSD hard-drive would be best to buy - 32 GB should be enough, price limit for SSD is up to 1000 USD, for controller same.

I am considering to buy Intel X25-E SSD, but I saw some good results with Patriot or OCZ Vertex...

According http://it-blog.5amsolutions.com/2010/08/performance-of-postgresql-ssd-vs.html there is really big performance step over using "standard" hard drives.

Thanks for any help.

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Do you have a ballpark figure on the percentage of queries that are SELECTs versus INSERT/UPDATE/DELETEs? –  Lars Haugseth Sep 14 '10 at 13:50

4 Answers 4

The Intel drives are known to have write caching that violates PostgreSQL (and other database) expectations; see Reliability section of the documentation for details on what those are. They don't flush their write cache out when the OS executes a normal fsync call, which is normal for SATA drives. And this will result in database corruption if the server crashes due to a power interruption. The only real option is to therefore turn the write cache off completely, and if you do that you'll discover the performance is terrible; the expected longevity of the drive plummets too. Some have reported even then it doesn't work right. See SSD, XFS, LVM, fsync, write cache, barrier and lost transactions for more information.

The recently released OCZ Vertex 2 Pro drives using a Sandforce controller and having an Ultracap battery backup are the first relatively inexpensive SSD model to reach the market worth considering here. That's passed all of the reliability tests those of us on the PostgreSQL Performance mailing list have come up for stressing this type of device, the Intel drives failed miserably. See Testing Sandforce SSD for benchmarks and reliability test information. There are some much more expensive "enterprise" SSDs that work fine as well, but those are all multi-thousand dollar devices. Note that you must be careful to get the Vertex 2 Pro, the cheaper Vertex models will not have the required Ultracap that makes this all work.

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Thanks for sharing your experiences, seeing OCZ coming on top of SSD reliability certainly raises a few eyebrows ;) –  Michael Renner Jan 8 '12 at 0:42

Do you really want to use an ssd, which have a lifespan limited by the number of writes, on a disk intensive system? Yes you will see a performance increase, but you will likely experience more disk failures and have to replace disks alit more often.

Have you looked at the performance of your database using fast 15k SAS drives? Remember your disk controller also has an impact on this. From expeience getting a high quality RAID controller can make a big difference.

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SSDs are not synonymous with Flash memory (which has a very limited no of writes) but trying to find a good cmos ssd these days is like finding a needle in a haystack –  symcbean Sep 14 '10 at 12:15
    
Intel X25-E drives are rated for 1PB of random 4k writes for the 32GB model. Intel X25-M drives are rated for up to 20GB/day for 5 years. If you're doing a high number of small IOPs to a single disk, then you may see SSDs wear out soon, but I don't think it's true across the board that the write longevity of a modern SSD is a cause for concern. –  Daniel Lawson Sep 30 '10 at 3:36

Sam,

thanks for nice answer, I read about SSD lifespan here: http://www.storagesearch.com/ssdmyths-endurance.html - that's why I am choosing Intel X25e, which should be enough situated for this. Now I got 10k RPM SAS Drive, and I want to also try different setup, so...

Which RAID controller for SSD (it is SATA, I mean Intel...) do you suggest ?

Also t answer Lars, I got around 5% update/inserts, most of use are selects.

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osij2is: I checked links, but I don't see any reason, why I should buy SandForce. Specially check this: pcper.com/article.php?aid=911&type=expert&pid=7 - Intel is still winning in IO test, which is the most important within DB. –  2ge Sep 16 '10 at 3:55
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I think data integrity is probably the most important concern within a DB environment? :) –  Daniel Lawson Sep 30 '10 at 3:33

Just to offer a different idea, I'd add that SandForce controllers are extremely good in contrast to Intel SSDs. I'd look into the controller and whether or not you can have TRIM support (I think with Linux it depends on your kernel version 2.6.??; I have no idea about BSD support) . Here's a great roundup article on SandForce SSDs from PCPerspective (http://www.pcper.com/article.php?aid=911) and about OCZ's firmware update that increased storage by 20% (http://www.pcper.com/article.php?aid=912)

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