<div>Dear Lars,</div>
<div> </div>
<div>The backend devices are on a <a class="l" onmousedown="return clk(this.href,'','','res','5','')" href="http://www-132.ibm.com/webapp/wcs/stores/servlet/ProductDisplay?productId=4611686018425211442&storeId=1&langId=-1&catalogId=-840"><font color="#0000cc">IBM <b>ServeRAID</b>-<b>8k</b> SAS <b>Controller</b> </font></a></div>
<div>with 256MB battery backed write cache</div>
<div> </div>
<div>you are saying i should not have seen a performence hit with a </div>
<div>battery backed write cache?</div>
<div> </div>
<div>i now tried with internal metada , options :</div>
<div> no-disk-flushes;<br> no-md-flushes;</div>
<div><br> and it now works almost to naive speed.</div>
<div> </div>
<div>results are similar as when i had the meta data on separate storage but </div>
<div>still leaving disk flushes and md flushes on. </div>
<div> </div>
<div>so i dont understand , does it request a flush from the backend device every write request ? it sounds like synchronous write...</div>
<div> </div>
<div>Also i read that if i do have a reliable battery backed write cache </div>
<div>i can use no-disk-flushes; no-md-flushes; , but i wonder if it is only the controller (with the battery backed write cache) that has protection?</div>
<div> </div>
<div>Don't hardrives have their own volatile write cache of their own ? </div>
<div> </div>
<div>so in a case the controller passed the data to the HD but the hd kept it in its cache and there was a power outage i would get corruption?<br><br></div>
<div class="gmail_quote">On Fri, Jun 20, 2008 at 3:45 PM, Lars Ellenberg <<a href="mailto:lars.ellenberg@linbit.com">lars.ellenberg@linbit.com</a>> wrote:<br>
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<div></div>
<div class="Wj3C7c">On Thu, Jun 19, 2008 at 09:28:58PM +0200, Marcelo Azevedo wrote:<br>> After placing the metadata on a different spindle (HD) , i was able to reach<br>> almost close to native speed (1-2MB/s less)<br>
><br>> with metadata internal i was reaching tops around half of the native speed ,<br>> 37MB/s~ :<br>> physical partition -> drbd -> ext3<br>> and<br>> 63MB/s~ with physical partition -> ext3<br>
> 61MB/s with metadata external, now this is true for another strong machine .<br>><br>> This other machine has hardware RAID1 with two :<br>> Cheetah T10 series,<br>> 146GB ,Serial Attached SCSI<br>> Interface Speed: 3Gb/s<br>
> Spindle Rotation Speed: 15,000 RPM<br>> Performance: 10K<br>> on an IBM 2G Xeon server with 2 dual cpu packages , each cpu with 4 cores . IBM<br>> ServeRAID SCSI controllers<br>> 4GB of ram<br>> native speed -hardware raid1 -> physical partition -> ext3 is around 110MB/s<br>
> ( still isn't this a bit slow for this HD ? )<br>> hardware raid1 -> physical partition -> drbd -> ext3 - 101MB/s with<br>> external metadata on a USB2 connected SATA HD 7,200 rpm<br>><br>> now this is the crazy part - 8.3MB/s~ write speed ! with internal metadata ,<br>
> and 150MB/s read speed..<br>> this test was repeated with bonnie , iozone and dd , all showed around same<br>> numbers ,<br>> i mean why the huge jump from 8MB/s to 100MB/s when using external metadata ,<br>
> and should this be STRESSED on the Docs or when starting the program that<br>> putting the metadata on external media improves performance significantly? ,<br>> still i don't understand why i was able to reach only 8MB/s write speed on this<br>
> strong server , maybe because of the hardware raid1 underneath?<br><br></div></div><a href="http://www.drbd.org/users-guide/ch-internals.html#s-metadata" target="_blank">http://www.drbd.org/users-guide/ch-internals.html#s-metadata</a><br>
-> internal meta data<br> -> disadvantages<br><br>"head movements" aka seek time.<br><br>if you use internal meta data on the same single spindle,<br>without a decent battery backed write cache,<br>you want to configure a large-ish al-extents,<br>
so drbd meta data updates happen infrequently.<br><br>--<br>: Lars Ellenberg <a href="http://www.linbit.com/" target="_blank">http://www.linbit.com</a> :<br>: DRBD/HA support and consulting sales at <a href="http://linbit.com/" target="_blank">linbit.com</a> :<br>
: LINBIT Information Technologies GmbH Tel +43-1-8178292-0 :<br>: Vivenotgasse 48, A-1120 Vienna/Europe Fax +43-1-8178292-82 :<br>__<br>please don't Cc me, but send to list -- I'm subscribed<br>_______________________________________________<br>
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