ProLiant Servers (ML,DL,SL)
cancel
Showing results for 
Search instead for 
Did you mean: 

Slow write to raid 5

graham findlay_1
Occasional Visitor

Slow write to raid 5

Ok we have a HP ProLiant ML370 G6 brand new with Server 2008 and 6gb ram

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.
10 REPLIES
Bleeder
Frequent Advisor

Re: Slow write to raid 5

If you don't have the optional battery kit for the onboard RAID, that could be the problem. No battery means no write caching. Also, even with the battery installed, you may still need to enable write caching via the array configuration utility.
graham findlay_1
Occasional Visitor

Re: Slow write to raid 5

Hi thanks for your reply.

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"

Bleeder
Frequent Advisor

Re: Slow write to raid 5

Unfortunately not all model servers come with the cache battery kit :-( I agree, they *should* come with it.

Best thing to do is open server case and check if there is a battery connected to the RAID card.
graham findlay_1
Occasional Visitor

Re: Slow write to raid 5

I know for a fact there is isn't

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
u84823
Regular Advisor

Re: Slow write to raid 5

Server '08 may treat writes differently as does vmware (in effective requiring BBWC for RAID). TBH it's a very cheap part in the scheme of things and you should certainly get it.

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).
Patrick Terlisten
Honored Contributor

Re: Slow write to raid 5

Hello,

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
Best regards,
Patrick
Bleeder
Frequent Advisor

Re: Slow write to raid 5

The problem is that HP, unlike certain other competing vendors, does not allow you to enable the RAID controller write cache without the battery kit installed. So, really, the customer does *not* have a choice, other than to choose a new vendor, or pay extra for a battery kit that should not be necessary.
Patrick Terlisten
Honored Contributor

Re: Slow write to raid 5

Hello,

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
Best regards,
Patrick
Taifur
Respected Contributor

Re: Slow write to raid 5

Hi,

U can check this issue by upgrading array controller firmware which is available in HP site

Rgds//
Taifur
Bleeder
Frequent Advisor

Re: Slow write to raid 5

In my organizations case, we have UPS battery backup for all of our server, plus a generator. Therefore, requiring a separate battery in order to simply enable write cache is redundant and a waste of precious budget monies.