fix: increase the tiering part size to 128MiB (#19424)

also introduce 8MiB buffer to read from for
bigger parts

internal/ioutil/ioutil.go

@@ -34,28 +34,35 @@ import (
 
 // Block sizes constant.
 const (
-	BlockSizeSmall       = 32 * humanize.KiByte // Default r/w block size for smaller objects.
-	BlockSizeLarge       = 1 * humanize.MiByte  // Default r/w block size for normal objects.
-	BlockSizeReallyLarge = 4 * humanize.MiByte  // Default r/w block size for very large objects.
+	SmallBlock   = 32 * humanize.KiByte // Default r/w block size for smaller objects.
+	LargeBlock   = 1 * humanize.MiByte  // Default r/w block size for normal objects.
+	XLargeBlock  = 4 * humanize.MiByte  // Default r/w block size for very large objects.
+	XXLargeBlock = 8 * humanize.MiByte  // Default r/w block size for very very large objects.
 )
 
 // aligned sync.Pool's
 var (
+	ODirectPoolXXLarge = sync.Pool{
+		New: func() interface{} {
+			b := disk.AlignedBlock(XXLargeBlock)
+			return &b
+		},
+	}
 	ODirectPoolXLarge = sync.Pool{
 		New: func() interface{} {
-			b := disk.AlignedBlock(BlockSizeReallyLarge)
+			b := disk.AlignedBlock(XLargeBlock)
 			return &b
 		},
 	}
 	ODirectPoolLarge = sync.Pool{
 		New: func() interface{} {
-			b := disk.AlignedBlock(BlockSizeLarge)
+			b := disk.AlignedBlock(LargeBlock)
 			return &b
 		},
 	}
 	ODirectPoolSmall = sync.Pool{
 		New: func() interface{} {
-			b := disk.AlignedBlock(BlockSizeSmall)
+			b := disk.AlignedBlock(SmallBlock)
 			return &b
 		},
 	}