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[Qemu-devel] [PATCH] Increase default qcow cluster size to 4KB
From: |
Anthony Liguori |
Subject: |
[Qemu-devel] [PATCH] Increase default qcow cluster size to 4KB |
Date: |
Mon, 19 Jun 2006 17:16:28 -0500 |
User-agent: |
Thunderbird 1.5.0.4 (X11/20060612) |
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;
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