That said, I think thin-provisioning in tgtd should only be available when the user specifies it explicitely. But as you say, end-users can often control whether the UNMAP command is used or not, often when mounting the filesystem on the initiator and this might be sufficient. I have no strong feelings either or. If you want this to be on by default and let the initiators decide on the matter, I am fine with that and can send you an updated patch that makes it available by default. regards ronnie sahlberg On Mon, Apr 2, 2012 at 10:50 AM, ronnie sahlberg <ronniesahlberg@xxxxxxxxx> wrote: > Hi, > > I think it should only be available if the user explicitely activates > it on the LUN. > The reason is that thin-provisioning is a bit dangerous if you are not careful. > > When using thin-provisioning you have to constantly monitor the > underlying filesystem and that it is not running out of space. > Because if the underlying filesystem becomes full, and WRITE10 calls > start failing, bad things will happen :-) > > > > When using thin-provisioning, this should be done by a concious > choice, and the user should be aware of the risks > and the need to monitor that the filesystem does not become full. > > I will write this up in a separate patch to the manpage to discuss the > pros and cons of thin provisioning and the risks associated with it > unless one is careful. > > > We should also in a later patch implement 4.7.3.8.1 tresholds so that > tgtd can tell thin-provisioning aware initiators when we are about to > run out of space so that those initiators can produce BIG warnings > to the admin to "take action before it is too late" . > > > > regards > ronnie sahlberg > > > On Mon, Apr 2, 2012 at 10:26 AM, FUJITA Tomonori > <fujita.tomonori@xxxxxxxxxxxxx> wrote: >> On Mon, 02 Apr 2012 09:06:11 +0900 (JST) >> FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: >> >>> On Sun, 1 Apr 2012 08:26:27 +1000 >>> ronnie sahlberg <ronniesahlberg@xxxxxxxxx> wrote: >>> >>>> From 2830abc3935294eba621b781f72aecda604c65a7 Mon Sep 17 00:00:00 2001 >>>> From: Ronnie Sahlberg <ronniesahlberg@xxxxxxxxx> >>>> Date: Sun, 1 Apr 2012 08:04:06 +1000 >>>> Subject: [PATCH 2/2] SBC UNMAP: Add support for thin-provisioning and the UNMAP command. >>>> >>>> The UNMAP command is implemented using FALLOC_FL_PUNCH_HOLE and will >>>> release UNMAPPED blocks back to the underlying filesystem. >>>> >>>> FALLOC_FL_PUNCH_HOLE is fairly new addition to Linux but works on >>>> ext4 and XFS filesystems currently. >>>> >>>> Signed-off-by: Ronnie Sahlberg <ronniesahlberg@xxxxxxxxx> >>>> --- >>>> doc/tgtadm.8.xml | 25 ++++++++++++++ >>>> usr/bs_rdwr.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>>> usr/sbc.c | 76 +++++++++++++++++++++++++++++++++++++++++- >>>> usr/scsi.h | 1 + >>>> usr/spc.c | 43 +++++++++++++++++++++-- >>>> usr/target.c | 2 + >>>> usr/tgtd.h | 2 + >>>> 7 files changed, 241 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/doc/tgtadm.8.xml b/doc/tgtadm.8.xml >>>> index 668e184..a40f659 100644 >>>> --- a/doc/tgtadm.8.xml >>>> +++ b/doc/tgtadm.8.xml >>>> @@ -352,6 +352,31 @@ tgtadm --lld iscsi --mode logicalunit --op update --tid 1 --lun 1 \ >>>> --params readonly=1 >>>> </screen> >>>> >>>> + <varlistentry><term><option>thin_provisioning=<0|1></option></term> >>>> + <listitem> >>>> + <para> >>>> + This controls the provisioning for the LUN. A thin-provisioned >>>> + LUN is represented as a sparse file. >>>> + TGTD supports provisioning type 2 for sparse files. >>>> + When initiators use the SCSI UNMAP command TGTD will release >>>> + the affected areas back to the filesystem using >>>> + FALLOC_FL_PUNCH_HOLE. >>>> + </para> >>>> + <para> >>>> + This parameter only applies to DISK devices. >>>> + </para> >>>> + <para> >>>> + Thin-provisioning only works for LUNs stored on filesystems >>>> + that support FALLOC_FL_PUNCH_HOLE. >>>> + </para> >>>> + </listitem> >>>> + </varlistentry> >>>> + >>>> + <screen format="linespecific"> >>>> +tgtadm --lld iscsi --mode logicalunit --op update --tid 1 --lun 1 \ >>>> + --params thin_provisioning=1 >>>> + </screen> >>> >>> Users need to enable this explicitly? >>> >>> I mean that when a lu is added, tgtd can check if the backing storage >>> supports FALLOC_FL_PUNCH_HOLE then enables it automatically? >> >> Note that I'm not against providing the explict option to users but >> normally users has the option for this (e.g. btrfs mount option) on >> the initiator side. So even if tgtd automatically enables this, users >> can avoid using this feature. So I wonder that it's worth providing >> the explict option. -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
