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Thu, 2 Mar 2023 18:34:04 +0100 (CET) MIME-Version: 1.0 Date: Thu, 02 Mar 2023 18:34:04 +0100 From: Gionatan Danti To: LVM general discussion and development In-Reply-To: References: <2023967259.761825.1677710640334.JavaMail.zimbra@karlsbakk.net> Message-ID: <17a0cca9c38c6eb8384275f68a2b465f@assyoma.it> X-Sender: g.danti@assyoma.it X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Subject: Re: [linux-lvm] lvconvert --uncache takes hours X-BeenThere: linux-lvm@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: LVM general discussion and development Cc: Roger Heflin , Malin Bruland Errors-To: linux-lvm-bounces@redhat.com Sender: "linux-lvm" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Il 2023-03-02 01:51 Roger Heflin ha scritto: > A spinning raid6 array is slow on writes (see raid6 write penalty). > Because of that the array can only do about 100 write operattions/sec. True. But does flushing cached data really proceed in random LBA order (as seen by HDDs), rather than trying to coalesce writes in linear fashion? > If the disk is doing other work then it only has the extra capacity so > it could destage slower. > > A lot depends on how big each chunk is. The lvmcache indicates the > smallest chunksize is 32k. > > 100G / 32k = 3 million, and at 100seeks/sec that comes to at least an > hour. You are off an order of magnitude: 3 millions IOP at 100 IOPs means ~30000s, so about 9 hours. > Lvm bookkeeping has to also be written to the spinning disks I would > think, so 2 hours if the array were idle. > > Throw in a 50% baseload on the disks and you get 4 hours. > > Hours is reasonable. If flushing happens in random disk order, than yes, you are bound to wait several hours indeed. Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@assyoma.it - info@assyoma.it GPG public key ID: FF5F32A8 _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://listman.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/