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тАО01-29-2010 04:24 AM
тАО01-29-2010 04:24 AM
Slow write to raid 5
We have 2 drives in Raid 1 for OS working fine.
We have 6 Drives in Raid 5 which have abysmally slow writes to them, I mean just very very slow. We have tried reformatting the logical drive and it still has the same performance. We have phoned HP and run through lots of diagnostics from smart start CD and they all pass. They have now esculated to the 2nd level but may take another 48 hours to get back to us!!
Has anybody any tips as to what the problem might be? We do not have the battery-backed write cache that HP keep on harping on about but as far as I am concerned this should only be needed for a performance boost not for normal operation.
Please if anybody can help that would be appreciated.
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тАО01-29-2010 08:03 AM
тАО01-29-2010 08:03 AM
Re: Slow write to raid 5
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тАО01-29-2010 08:18 AM
тАО01-29-2010 08:18 AM
Re: Slow write to raid 5
I do not get this. What you are saying is that the battery is not optional?
I guess I expect to purchase a server and for the drives to have good I/O without having to buy an "optional extra"
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тАО01-29-2010 08:20 AM
тАО01-29-2010 08:20 AM
Re: Slow write to raid 5
Best thing to do is open server case and check if there is a battery connected to the RAID card.
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тАО01-29-2010 09:05 AM
тАО01-29-2010 09:05 AM
Re: Slow write to raid 5
but according to this article
http://articles.techrepublic.com.com/5100-10878_11-6064529.html
and many othere it isn't needed for "normal" performance
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тАО02-01-2010 04:13 AM
тАО02-01-2010 04:13 AM
Re: Slow write to raid 5
However I would question this disk config anyway, the machine will perform MUCH better as an 8-drive RAID-10 (random write would be 2.6x faster and random read 60% faster).
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тАО02-01-2010 04:35 AM
тАО02-01-2010 04:35 AM
Re: Slow write to raid 5
first of all: You should put all disks into one array and then create logical drives. In this case the data is distributed over 8, not only 2 disks.
The write performance of a RAID 5 can be really poor. Ony 25% of the write IOPS can really be used, the other 75% are overhead. This is called "write penalty". RAID 5 is nice if you have more reads then writes, but not if you have a lot of small write IOs.
Sure, HP should sell all servers with a BBWC, but some customers are quite economical and they don't want a BBWC and they don't want to pay a part of a server they don't want. So the customer has the choice. If the customer doesn't have enough knowledge, the reseller should help him.
Just my 2 cents...
Regards,
Patrick
Patrick
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тАО02-02-2010 12:45 PM
тАО02-02-2010 12:45 PM
Re: Slow write to raid 5
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тАО02-02-2010 11:18 PM
тАО02-02-2010 11:18 PM
Re: Slow write to raid 5
other vendors may activate write cache, but what in case of a power failure? Data may be lost. What is the value of you data? A BBWC doesn't cost much and you have the choice to buy it or not. It's not HPs fault. But the decision, to disable write cache without a BBWC, is much more secure, then enable it without a BBWC.
Regards,
Patrick
Patrick
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тАО02-02-2010 11:25 PM
тАО02-02-2010 11:25 PM
Re: Slow write to raid 5
U can check this issue by upgrading array controller firmware which is available in HP site
Rgds//
Taifur