Re: [PERFORM] 8x2.5 or 6x3.5 disks
I missed the initial post in this thread, but I haven't seen any 15K rpm 2.5 drives, so if you compare 10K rpm 2.5 drives with 15K rpm 3.5 drives you will see differences (depending on your workload and controller cache) I have some 15K rpm 2.5 sas-drives from HP. Other vendors have them as well. -- regards Claus When lenity and cruelty play for a kingdom, the gentlest gamester is the soonest winner. Shakespeare ---(end of broadcast)--- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
Re: [PERFORM] 8x2.5 or 6x3.5 disks
You don't mention the capacity of the disks you are looking at. Here is something you might want to consider. I've seen a few performance posts on using different hardware technologies to gain improvements. Most of those comments are on raid, interface and rotation speed. One area that doesn't seem to have been mentioned is to run your disks empty. One of the key roadblocks in disk performance is the time for the disk heads to seek, settle and find the start of the data. Another is the time to transfer from disk to interface. Everyone may instinctively know this but its often ignored. Hard disks are CRV ( constant rotational velocity) = they spin at the same speed all the time Hard disk drives use a technology called ZBR = Zone Bit Recording = a lot more data on the outside tracks than the inner ones. Hard disk fill up from outside track to inside track generally unless you've done some weird partitioning. On the outside of the disk you get a lot more data per seek than on the inside. Double whammy you get it faster. Performance can vary more than 100% between the outer and inner tracks of the disk. So running a slower disk twice as big may give you more benefit than running a small capacity 15K disk full. The slower disks are also generally more reliable and mostly much cheaper. The other issue for full disks especially with lots of random small transactions is the heads are seeking and settling across the whole disk but typically with most of those seeks being on the latest transactions which are placed nicely towards the middle of the disk. I know of a major bank that has a rule of thumb 25% of the disk partioned as a target maximum for high performance disk systems in a key application. They also only pay for used capacity from their disk vendor. This is not very green as you need to buy more disks for the same amount of data and its liable to upset your purchasing department who won't understand why you don't want to fill your disks up. Mike
Re: [PERFORM] 8x2.5 or 6x3.5 disks
There are several suppliers who offer Seagate's 2.5 15k rpm disks, I know HP, Dell are amongst those. So I was actually refering to those, rather than to the 10k one's. Best regards, Arjen [EMAIL PROTECTED] wrote: On Mon, 28 Jan 2008, Arjen van der Meijden wrote: On 28-1-2008 20:25 Christian Nicolaisen wrote: So, my question is: should I go for the 2.5 disk setup or 3.5 disk setup, and does the raid setup in either case look correct? Afaik they are about equal in speed. With the smaller ones being a bit faster in random access and the larger ones a bit faster for sequential reads/writes. I missed the initial post in this thread, but I haven't seen any 15K rpm 2.5 drives, so if you compare 10K rpm 2.5 drives with 15K rpm 3.5 drives you will see differences (depending on your workload and controller cache) David Lang ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PERFORM] 8x2.5 or 6x3.5 disks
Mike Smith wrote: I’ve seen a few performance posts on using different hardware technologies to gain improvements. Most of those comments are on raid, interface and rotation speed. One area that doesn’t seem to have been mentioned is to run your disks empty. ... On the outside of the disk you get a lot more data per seek than on the inside. Double whammy you get it faster. Performance can vary more than 100% between the outer and inner tracks of the disk. So running a slower disk twice as big may give you more benefit than running a small capacity 15K disk full. The slower disks are also generally more reliable and mostly much cheaper. ... This is not very green as you need to buy more disks for the same amount of data and its liable to upset your purchasing department who won’t understand why you don’t want to fill your disks up. So presumably the empty-disk effect could also be achieved by partitioning, say 25% of the drive for the database, and 75% empty partition. But in fact, you could use that low performance 75% for rarely-used or static data, such as the output from pg_dump, that is written during non-peak times. Pretty cool. Craig ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [PERFORM] 8x2.5 or 6x3.5 disks
[presumably the empty-disk effect could also be achieved by partitioning, say 25% of the drive for the database, and 75% empty partition. But in fact, you could use that low performance 75% for rarely-used or static data, such as the output from pg_dump, that is written during non-peak times] Larry Ellison financed a company called Pillar Data Systems which was founded on the principle that you can tier the disk according to the value and performance requirements of the data. They planned to put the most valuable in performance terms on the outside of SATA disks and use the empty space in the middle for slower stuff.. (This is not an advert. I like the idea but I dont know if it works well and I dont have anything to do with Pillar other than EnterpriseDB compete against Larry's other little company). Probably the way to go is flash drives for primary performance data . EMC and others have announced Enterprise Flash Drives (they claim 30 times performance of 15K disks although at 30 times the cost of standard disk today ). Flash should also have pretty much consistent high performance across the whole capacity. Within a couple of years EFD should be affordable for mainstream use.
Re: [PERFORM] 8x2.5 or 6x3.5 disks
On 28-1-2008 20:25 Christian Nicolaisen wrote: So, my question is: should I go for the 2.5 disk setup or 3.5 disk setup, and does the raid setup in either case look correct? Afaik they are about equal in speed. With the smaller ones being a bit faster in random access and the larger ones a bit faster for sequential reads/writes. My guess is that the 8x 2.5 configuration will be faster than the 6x 3.5, even if the 3.5-drives happen to be faster they probably aren't 50% faster... So since you don't need the larger storage capacities that 3.5 offer, I'd go with the 8x 2.5-setup. Best regards, Arjen ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PERFORM] 8x2.5 or 6x3.5 disks
On Mon, 28 Jan 2008, Arjen van der Meijden wrote: On 28-1-2008 20:25 Christian Nicolaisen wrote: So, my question is: should I go for the 2.5 disk setup or 3.5 disk setup, and does the raid setup in either case look correct? Afaik they are about equal in speed. With the smaller ones being a bit faster in random access and the larger ones a bit faster for sequential reads/writes. I missed the initial post in this thread, but I haven't seen any 15K rpm 2.5 drives, so if you compare 10K rpm 2.5 drives with 15K rpm 3.5 drives you will see differences (depending on your workload and controller cache) David Lang ---(end of broadcast)--- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
