Lines Matching +full:use +full:- +full:parity

7 caches data to the RAID disks. The cache can be in write-through (supported
8 since 4.4) or write-back mode (supported since 4.10). mdadm (supported since
9 3.4) has a new option '--write-journal' to create array with cache. Please
11 in write-through mode. A user can switch it to write-back mode by::
13 	echo "write-back" > /sys/block/md0/md/journal_mode
15 And switch it back to write-through mode by::
17 	echo "write-through" > /sys/block/md0/md/journal_mode
22 write-through mode
27 and parity don't match. The reason is that a stripe write involves several RAID
34 The write-through cache will cache all data on cache disk first. After the data
36 two-step write will guarantee MD can recover correct data after unclean
39 In write-through mode, MD reports IO completion to upper layer (usually
44 In write-through mode, the cache disk isn't required to be big. Several
47 write-back mode
50 write-back mode fixes the 'write hole' issue too, since all write data is
51 cached on cache disk. But the main goal of 'write-back' cache is to speed up
52 write. If a write crosses all RAID disks of a stripe, we call it full-stripe
53 write. For non-full-stripe writes, MD must read old data before the new parity
56 overhead too. Write-back cache will aggregate the data and flush the data to
61 In write-back mode, MD reports IO completion to upper layer (usually
66 In write-back mode, MD also caches data in memory. The memory cache includes
74 mode depending on the workloads. It's recommended to use a cache disk with at
75 least several gigabytes size in write-back mode.
80 The write-through and write-back cache use the same disk format. The cache disk
83 ID for recovery identification. Data can be IO data and parity data. Data is
91 write-through mode, MD calculates parity for IO data, writes both IO data and
92 parity to the log, writes the data and parity to RAID disks after the data and
93 parity is settled down in log and finally the IO is finished. Read just reads
96 In write-back mode, MD writes IO data to the log and reports IO completion. The
99 MD will calculate parity for the data and write parity into the log. After this
100 is finished, MD will write both data and parity into RAID disks, then MD can
102 stripe write, free cache disk space is low or free in-kernel memory cache space
107 data and data. If MD finds a stripe with data and valid parities (1 parity for