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dasdfmt: Change mode default

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When formatting an ESE (thin-provisioned) ECKD DASD, dasdfmt(8)
defaults to the quick-format mode instead of full-format for normal
DASDs. This results in a significant performance impact during first
sequential write to each track, which may be unexpected for users.

To address this, change the default for dasdfmt to always use
full-format mode. Customers that require thin provisioning(*) still
override the default by specifying quick format explicitly using the
"-M" option.

Get rid of the related fallbacks; In case of unsuccessful space
release always fail. The customers that still require quick format can
proceed by specifying "--no-discard" option.

(*) Thin provisioning: while providing a large amount of logical
    space, zero amount of actual space is provisioned and then
    allocated on an on-demand basis.

Signed-off-by: Eduard Shishkin <edward6@linux.ibm.com>
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
This commit is contained in:
Eduard Shishkin
2024-02-19 17:25:04 +01:00
committed by Jan Höppner
parent c47071815b
commit 998b61e5f3
2 changed files with 15 additions and 28 deletions
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18
dasdfmt/dasdfmt.8
View File

@@ -118,16 +118,16 @@ Specify the \fImode\fR to be used to format the device. Valid modes are:
.IP full
Format the entire disk with the specified blocksize. (default)
.IP quick
Format the first two tracks and write label and partition information. Use this
option only if you are sure that the target DASD already contains a regular
format with the specified blocksize. A blocksize can optionally be specified
using \fB-b\fR (\fB--blocksize\fR).
Format the first two tracks and write label and partition information.
.br
For thin-provisioned DASD ESE volumes, quick is the default mode. A full space
release then precedes the formatting step. If this space release fails, dasdfmt
falls back to a full-format mode. Formatting stops if the space release fails
and quick mode was specified explicitly using \fB-M\fR. Specify the
\fB--no-discard\fR option to omit the space release.
Use this option for DASD ESE volumes to take the benefits of thin provisioning.
In this case, a full space release precedes the formatting step. If this space
release fails, then the formatting also fails. Specify the \fB--no-discard\fR
option to omit the space release.
.br
For non-ESE volumes use this option only if you are sure that the target DASD
already contains a regular format with the specified blocksize. A blocksize can
optionally be specified using \fB-b\fR (\fB--blocksize\fR).
.IP expand
Format all unformatted tracks at the end of the target DASD. This mode assumes

25
dasdfmt/dasdfmt.c
View File

@@ -1230,7 +1230,7 @@ static void dasdfmt_find_start(unsigned int cylinders, unsigned int heads,
format_params->start_unit = first;
}
static int dasdfmt_release_space(void)
static void dasdfmt_release_space(void)
{
format_data_t r = {
.start_unit = 0,
@@ -1240,21 +1240,12 @@ static int dasdfmt_release_space(void)
int err = 0;
if (!g.ese || g.no_discard)
return 0;
return;
printf("Releasing space for the entire device...\n");
err = dasd_release_space(g.dev_node, &r);
/*
* Warn or Error on failing RAS depending on QUICK mode set explicitly or automatically
*/
if (err && !g.mode_specified) {
warnx("Could not release space. Falling back to full format.");
return 1;
} else if (err && g.mode_specified) {
if (err)
error("Could not release space: %s", strerror(err));
}
return 0;
}
static void dasdfmt_prepare_and_format(unsigned int cylinders, unsigned int heads,
@@ -1454,12 +1445,8 @@ static void do_format_dasd(volume_label_t *vlabel, format_data_t *p,
dasdfmt_prepare_and_format(cylinders, heads, p);
break;
case QUICK:
if (dasdfmt_release_space()) {
p->stop_unit = (cylinders * heads) - 1;
dasdfmt_prepare_and_format(cylinders, heads, p);
} else {
dasdfmt_quick_format(cylinders, heads, p);
}
dasdfmt_release_space();
dasdfmt_quick_format(cylinders, heads, p);
break;
case EXPAND:
dasdfmt_expand_format(cylinders, heads, p);
@@ -1491,7 +1478,7 @@ static void eval_format_mode(void)
}
if (!g.mode_specified)
mode = g.ese ? QUICK : FULL;
mode = FULL;
}
/*