[Qemu-devel] [PATCH] Increase default qcow cluster size to 4KB

[Anthony Liguori]

Regards,

Anthony Liguori

# HG changeset patch
# User Anthony Liguori <address@hidden>
# Node ID 76bb5704c9afe3fb930e81e13fd6de57b452ff5c
# Parent  4fcb5f2d8d8646e56ddb2f6bac4d457b66fdb8ab
Change default cluster size for qcow disks to 4KB.  This size makes it much
easier for implementing high-performance qcow backends (for things like Xen)
as the kernel tends to like to deal with reads/writes in at least 4K chunks.

diff -r 4fcb5f2d8d86 -r 76bb5704c9af block-qcow.c
--- a/block-qcow.c      Mon Jun 19 00:41:28 2006 +0000
+++ b/block-qcow.c      Mon Jun 19 17:14:52 2006 -0500
@@ -574,13 +574,10 @@ static int qcow_create(const char *filen
        } else
            backing_file = NULL;
         header.mtime = cpu_to_be32(st.st_mtime);
-        header.cluster_bits = 9; /* 512 byte cluster to avoid copying
-                                    unmodifyed sectors */
-        header.l2_bits = 12; /* 32 KB L2 tables */
-    } else {
-        header.cluster_bits = 12; /* 4 KB clusters */
-        header.l2_bits = 9; /* 4 KB L2 tables */
-    }
+    }
+    header.cluster_bits = 12; /* 4 KB clusters */
+    header.l2_bits = 9; /* 4 KB L2 tables */
+
     header_size = (header_size + 7) & ~7;
     shift = header.cluster_bits + header.l2_bits;
     l1_size = ((total_size * 512) + (1LL << shift) - 1) >> shift;