From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dirk Geschke Subject: bcache not working on large files? Date: Tue, 22 Oct 2013 09:08:30 +0200 Message-ID: <20131022070830.GA20286@euve30603.vserver.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org Hi all, I was just playing a little bit with bcache and it works fine. But if I try random IOPS writes (writeback) on a file larger than the cache, it seems not to work? At least I get a performance as without bcache. I used a RAID-6 of 8 SSDs (each 238 GiB) as a cache and a RAID-6 of 10 HDDs (2794 Gib). For my test I did random writes of 4k blocks. With 8 threads writing on one 1000 GB file, I get IOPS in the range of 20000, but with a file of 10000 GB I end up with about 400 IOPS. That is the same as without cache. Did I miss something? Is caching disabled in such cases? I would expect, that even in this case (writeback and random writes) it should work as well. Even after a few minutes I get these results, so it is not a problem of a full cache. Has anyone a hint for me, what is going wrong? Best regards Dirk -- +----------------------------------------------------------------------+ | Dr. Dirk Geschke / Plankensteinweg 61 / 85435 Erding | | Telefon: 08122-559448 / Mobil: 0176-96906350 / Fax: 08122-9818106 | | dirk-tpR6ahGJfjwEZ6m2XrtfILNAH6kLmebB@public.gmane.org / dirk-WMiem5eIfR0n5izryJqWLw@public.gmane.org / kontakt-WMiem5eIfR0n5izryJqWLw@public.gmane.org | +----------------------------------------------------------------------+