Re: SSD Drives
От | Steve Crawford |
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Тема | Re: SSD Drives |
Дата | |
Msg-id | 533F2AD6.3050208@pinpointresearch.com обсуждение исходный текст |
Ответ на | Re: SSD Drives (Merlin Moncure <mmoncure@gmail.com>) |
Ответы |
Re: SSD Drives
(David Boreham <david_list@boreham.org>)
|
Список | pgsql-general |
On 04/04/2014 10:15 AM, Merlin Moncure wrote: >> 2. Do I need both BBU on the RAID *and* capacitor on the SSD or just on one? >> Which one? I'm suspecting capacitor on the SSD and write-through on the >> RAID. > You need both. The capacitor protects the drive, the BBU protects the > raid controller. ?? In write-through the controller shouldn't return success until it gets it from the drive so no BBU should be required. One LSI slide deck recommends write-back as the optimum policy for SSDs. But I could be wrong which is why I ask. >> 2. Current thoughts on hardware vs. software RAID - especially since many of >> the current SSD solutions plug straight into the bus. > IMNSHO, software raid is a better bet. The advantages are compelling: > Cost, TRIM support, etc. and the SSD drives do not benefit as much > from the write cache. But hardware controllers offer very fast burst > write performance which is nice. > > 6. Thoughts on "best bang for the buck?" For example, am I better off > dropping the RAID cards and additional drives and instead adding another > standby server? > This is going to depend a lot on write patterns. If you don't do much > writing, you can gear up accordingly. For all around performance, the > S3700 (2.5$/gb) IMO held the crown for most of 2013 and I think is > still the one to buy. The s3500 (1.25$/gb) came out and also looks > like a pretty good deal, and there are some decent competitors (600 > pro for example). If you're willing to spend more, there are a lot of > other options. I don't think it's reasonable to spend less for a > write heavy application. FWIW, the workload is somewhat over 50% writes and currently peaks at ~1,600 queries/second after excluding "set" statements. This is currently spread across four 15k SATA drives in RAID 10. Judicious archiving allows us to keep our total OS+data storage requirements under 100GB. Usually. So we should be able to easily stay in the $500/drive price range (200GB S3700) and still have plenty of headroom for wear-leveling. One option I'm considering is no RAID at all but spend the savings from the controllers and extra drives toward an additional standby server. Cheers, Steve
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