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Terrible Write Performance on Smart Array p400i

Eric Coan
Occasional Visitor

Terrible Write Performance on Smart Array p400i

I am trying to find a fix for the write performance issue I am experiencing on a ProLiant DL360 G5 server equipped with a smart array p400i raid controller.

Currently I am getting write speeds of about 3MB/sec. Which gives my old 486 a run for it's money.

In researching the issue and spending over an hour on HP tech support I understand that supposedly a BBWC module is required to turn on write caching and make the machine actually useful for something other than adding heat to the server room.

I have also heard that using the hpacucli command "cntrl slot=0 modify drivewritecache=enable" I should be able to turn the write caching feature on with out the BBWC module installed. The text from the command is:

Without the proper safety precautions, use of write cache on physical drives could cause data loss in the event of a power failure. To ensure data is properly protected, use redundant power supplies and Uninterruptible Power Supplies. Also, if you have multiple storage enclosures, all data should be mirrored across them. Use of this feature is not recommended unless these precautions are followed. Continue (y/n)

Entering "y" just results in this error:

Error: This operation is not supported with the current configuration. Use the "show" command on devices to show additional details about the configuration.

Now, the first message would seem to indicate that I can turn on the write cache without the BBWC but data loss might occur if power is cut during a write operation. That is fine with me since this is a test and not production system that I am using.

There have been a few threads on this topic already, I know. However it seems that the question of "can I turn the write caching ability on without the BBWC" is a maybe at best.

Also, if we have to order the part is part number 398648-001 the correct one? That is what the tech told me but he sounded unsure on the phone. I have also seen the part number 383280-B21 referenced.

Any and all help would be greatly appreciated!

As a side note, I am confused as to why HP would sell this $1700 server crippled by default to the point where my $500 workstation vastly out performs it on any task that involves writing data to disk. I understand the BBWC is a fail safe but in the "out of the box" configuration the machine is almost useless.
2 REPLIES
Eric de Lange (MSE)
Valued Contributor

Re: Terrible Write Performance on Smart Array p400i

Greets Eric,

What is the nature of your write perfomance issue ? What/how are you writing ? What results are you measuring, in terms of IO and response times.

What about writing a large (gigabyte sized) file to your array ? If that also shows bad performance then likely write cache (or the lack of) is not your issue.

let us know.

-Eric





Víctor Cespón
Honored Contributor

Re: Terrible Write Performance on Smart Array p400i

If it has a P400i, it must be a High Efficiency or Performance model.
From the sever Quickspecs:
http://h18004.www1.hp.com/products/quickspecs/12476_div/12476_div.html

- Performance Models: HP Smart Array P400i/256MB BBWC Controller (RAID 0/1/1+0/5/6) (512MB BBWC optional)
- High Efficiency and Base Models: HP Smart Array P400i/256MB Controller (RAID 0/1/1+0/5) (512MB BBWC optional)

Battery-backed write cache upgrade 383280-B21
512 MB Battery-backed write cache upgrade 405148-B21

The command you mention enables write caching on the drives, which have no internal battery, so if power is lost the data on the cache is lost. This can only be enabled on SATA disks.

3 MB/s is very slow even without write caching. How many disks are connected to that P400 and what model? Are you testing sequential or random write?