Very slow writes on flash + msdosfs

[Mark Day]

On Mac OS X (where msdosfs is derived from FreeBSD), I fixed it by  
just buffering up the I/O into 128KB chunks.  Simple but effective.   
The diffs are below, based on the Mac OS X sources.  But I'll bet it's  
not too hard to apply to FreeBSD; I don't think the newfs_msdos  
sources have diverged too much.  I hope this helps.

-Mark

Index: newfs_msdos.tproj/newfs_msdos.c
===================================================================
--- newfs_msdos.tproj/newfs_msdos.c     (revision 26754)
+++ newfs_msdos.tproj/newfs_msdos.c     (revision 26759)
@@ -73,6 +73,7 @@

  #define DOSMAGIC  0xaa55       /* DOS magic number */
  #define MINBPS   128           /* minimum bytes per sector */
+#define MAXBPS    4096         /* maximum bytes per sector */
  #define MAXSPC   128           /* maximum sectors per cluster */
  #define MAXNFT   16            /* maximum number of FATs */
  #define DEFBLK   4096          /* default block size */
@@ -81,6 +82,16 @@
  #define RESFTE   2             /* reserved FAT entries */

  /*
+ * The size of our in-memory I/O buffer.  This is the size of the  
writes we
+ * do to the device (except perhaps a few odd sectors at the end).
+ *
+ * This must be a multiple of the sector size.  Larger is generally  
faster,
+ * but some old devices have bugs if you ask them to do more than 128KB
+ * per I/O.
+ */
+#define IO_BUFFER_SIZE (128*1024)
+
+/*
   * [2873845]  FAT12 volumes can have 1..4084 clusters.  FAT16 can have
   * 4085..65524 clusters.  FAT32 is 65525 clusters or more.
   * Since many other implementations are off by 1, 2, 4, 8, 10, or 16,
@@ -312,7 +323,8 @@
      struct bsxbpb *bsxbpb;
      struct bsx *bsx;
      struct de *de;
-    u_int8_t *img;
+    u_int8_t *io_buffer;    /* The buffer for sectors being  
constructed/written */
+    u_int8_t *img;         /* Current sector within io_buffer */
      const char *fname, *dtype, *bname;
      ssize_t n;
      time_t now;
@@ -445,6 +457,9 @@
      if (bpb.bps < MINBPS)
         errx(1, "bytes/sector (%u) is too small; minimum is %u",
              bpb.bps, MINBPS);
+    if (bpb.bps > MAXBPS)
+       errx(1, "bytes/sector (%u) is too large; maximum is %u",
+            bpb.bps, MAXBPS);
      if (!(fat = opt_F)) {
         if (opt_f)
             fat = 12;
@@ -702,12 +717,13 @@
          bpb.sec = 0;
      }
      print_bpb(&bpb);
-    if (!opt_N) {
+    if (!opt_N) {
          gettimeofday(&tv, NULL);
          now = tv.tv_sec;
          tm = localtime(&now);
-        if (!(img = malloc(bpb.bps)))
+        if (!(io_buffer = malloc(IO_BUFFER_SIZE)))
              err(1, NULL);
+       img = io_buffer;
          dir = bpb.res + (bpb.spf ? bpb.spf : bpb.bspf) * bpb.nft;
         for (lsn = 0; lsn < dir + (fat == 32 ? bpb.spc : rds); lsn++) {
             x = lsn;
@@ -808,9 +824,21 @@
                     (u_int)tm->tm_mday;
                 mk2(de->date, x);
             }
-           if ((n = write(fd, img, bpb.bps)) == -1)
+           img += bpb.bps;
+           if (img >= (io_buffer + IO_BUFFER_SIZE)) {
+               /* We filled the I/O buffer, so write it out now */
+               if ((n = write(fd, io_buffer, IO_BUFFER_SIZE)) == -1)
+                   err(1, "%s", fname);
+               if (n != IO_BUFFER_SIZE)
+                   errx(1, "%s: can't write sector %u", fname, lsn);
+               img = io_buffer;
+           }
+       }
+       if (img != io_buffer) {
+           /* The I/O buffer was partially full; write it out before  
exit */
+           if ((n = write(fd, io_buffer, img-io_buffer)) == -1)
                 err(1, "%s", fname);
-           if (n != bpb.bps)
+           if (n != (img-io_buffer))
                 errx(1, "%s: can't write sector %u", fname, lsn);
         }
      }

On Oct 4, 2007, at 5:48 PM, Dmitry Marakasov wrote:

> Hi!
>
> I have USB flash:
>
> da0 at umass-sim0 bus 0 target 0 lun 0
> da0: <JetFlash TS2GJF150 8.07> Removable Direct Access SCSI-2 device
> da0: 40.000MB/s transfers
> da0: 1999MB (4095998 512 byte sectors: 255H 63S/T 254C)
>
> It attaches to ehci and I get pretty good read/write speed:
>
> % dd if=/dev/zero of=/dev/da0 bs=1m
> dd: /dev/da0: short write on character device
> dd: /dev/da0: end of device
> 2000+0 records in
> 1999+1 records out
> 2097150976 bytes transferred in 178.132363 secs (11772993 bytes/sec)
>
> % dd if=/dev/da0 of=/dev/zero bs=1m count=100
> 100+0 records in
> 100+0 records out
> 104857600 bytes transferred in 7.240738 secs (14481618 bytes/sec)
>
> But newfs_msdos ran on it is very slow:
>
> % time newfs_msdos -F32 -LAMDmi3 -k 0xffff /dev/da0s1
> /dev/da0s1: 4072456 sectors in 509057 FAT32 clusters (4096 bytes/ 
> cluster)
> bps=512 spc=8 res=32 nft=2 mid=0xf0 spt=63 hds=255 hid=0  
> bsec=4080447 bspf=3978 rdcl=2 infs=1 bkbs=0xffff
> newfs_msdos -F32 -LAMDmi3 -k 0xffff /dev/da0s1  0,02s user 0,21s  
> system 0% cpu 2:54,37 total
>
> when it runs, gkrellm shows 23kb/s writes.
>
> Writing a 1.0Mb directory with 340 files takes 1.5 minutes (up to  
> 300k/sec
> writes => seems like much more data is actually written that it's
> needed).
>
> Larger files behave somewhat better (up to 3 MB/s).
>
> Btw, dd if=/dev/zero of=/dev/da0 bs=512 show the same 23k/s speed as
> newfs_msdosfs.
>
> So where is the problem? Why's there no caching and why's there 1  
> sector
> writes?
>
> PS. I use 6.1, has the situation changed in -CURRENT?
>
> -- 
> Best regards,
>  Dmitry Marakasov               mailto:amdmi3 at amdmi3.ru
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