142
142
with the previous I/O request are enabled. When set to 2,
143
143
all merge tries are disabled. The default value is 0 -
144
144
which enables all types of merge tries.
146
What: /sys/block/<disk>/discard_alignment
148
Contact: Martin K. Petersen <martin.petersen@oracle.com>
150
Devices that support discard functionality may
151
internally allocate space in units that are bigger than
152
the exported logical block size. The discard_alignment
153
parameter indicates how many bytes the beginning of the
154
device is offset from the internal allocation unit's
157
What: /sys/block/<disk>/<partition>/discard_alignment
159
Contact: Martin K. Petersen <martin.petersen@oracle.com>
161
Devices that support discard functionality may
162
internally allocate space in units that are bigger than
163
the exported logical block size. The discard_alignment
164
parameter indicates how many bytes the beginning of the
165
partition is offset from the internal allocation unit's
168
What: /sys/block/<disk>/queue/discard_granularity
170
Contact: Martin K. Petersen <martin.petersen@oracle.com>
172
Devices that support discard functionality may
173
internally allocate space using units that are bigger
174
than the logical block size. The discard_granularity
175
parameter indicates the size of the internal allocation
176
unit in bytes if reported by the device. Otherwise the
177
discard_granularity will be set to match the device's
178
physical block size. A discard_granularity of 0 means
179
that the device does not support discard functionality.
181
What: /sys/block/<disk>/queue/discard_max_bytes
183
Contact: Martin K. Petersen <martin.petersen@oracle.com>
185
Devices that support discard functionality may have
186
internal limits on the number of bytes that can be
187
trimmed or unmapped in a single operation. Some storage
188
protocols also have inherent limits on the number of
189
blocks that can be described in a single command. The
190
discard_max_bytes parameter is set by the device driver
191
to the maximum number of bytes that can be discarded in
192
a single operation. Discard requests issued to the
193
device must not exceed this limit. A discard_max_bytes
194
value of 0 means that the device does not support
195
discard functionality.
197
What: /sys/block/<disk>/queue/discard_zeroes_data
199
Contact: Martin K. Petersen <martin.petersen@oracle.com>
201
Devices that support discard functionality may return
202
stale or random data when a previously discarded block
203
is read back. This can cause problems if the filesystem
204
expects discarded blocks to be explicitly cleared. If a
205
device reports that it deterministically returns zeroes
206
when a discarded area is read the discard_zeroes_data
207
parameter will be set to one. Otherwise it will be 0 and
208
the result of reading a discarded area is undefined.