no-read-back.txt

>>> one_gig = 1024*1024*1024
>>> thirty_two_gigs = one_gig * 32
>>> one_gig * 32 == thirty_two_gigs
True
>>> for i in range(thirty_two_gigs):
...    _ = f.write("\n")
...    if i % one_gig == 0: print(i)
... 
0
1073741824
2147483648
3221225472
4294967296
5368709120
6442450944
7516192768
8589934592
9663676416
10737418240
11811160064
12884901888
13958643712
15032385536
16106127360
17179869184
18253611008
19327352832
20401094656
21474836480
22548578304
23622320128
24696061952
25769803776
26843545600
27917287424
28991029248
30064771072
31138512896
32212254720
33285996544
>>> for _ in range(1024):
...     _ = f.write("A")
... 
>>> f = open("/dev/sda", "r")
>>> for i in range(thirty_two_gigs):
...     if f.read(1) == "A": print(i, "A")
...     if i % one_gig == 0: print(i)
... 
0
1073741824
2147483648
3221225472
4294967296
5368709120
6442450944
7516192768
8589934592
9663676416
10737418240
11811160064
12884901888
13958643712
15032385536
16106127360
17179869184
18253611008
19327352832
20401094656
21474836480
22548578304
23622320128
24696061952
25769803776
26843545600
27917287424
28991029248
30064771072
31138512896
32212254720
33285996544
>>> for i in range(thirty_two_gigs):
...     if f.read(1) == "A": print(i, "A")
...     if i % one_gig == 0: print(i)
... 
0
1073741824
2147483648
3221225472
^CTraceback (most recent call last):
  File "<stdin>", line 2, in <module>
KeyboardInterrupt
>>> 

First write 32GB of newlines, then 1KB of "A" chars. Read back 32G, then read back 3G more and note that "A" is not found.