Chookiex writes:
> Hi all,
>
> I have 2 questions about ZFS.
>
> 1. I have create a snapshot in my pool1/data1, and zfs send/recv it to
pool2/data2. but I found the USED in zfs list is different:
> NAME USED AVAIL REFER MOUNTPOINT
> pool2/data2 160G 1.44T 159G /pool2/data2
> pool1/data 176G 638G 175G /pool1/data1
>
> It keep about 30,000,000 files.
> The content of p_pool/p1 and backup/p_backup is almost same. But why is
the size different?
>
160G for 30M files means your avg file size is 5333 Bytes.
Pick one such files just for illustration: 5333 Bytes to be
stored on raid-z2 of 5 disks (3+2). So you have to store
5333 Bytes of data onto 3 data disks. You will need a stripe
of 4 x 512B sectors on each of the 3 data disks. So that''s
6K of data.
Over a single volume, you''d need 11 sectors of 512B to store
5632 Bytes.
For this avg file size you thus have either 12 or 11 sectors
to store the data, a 9% difference.
You then need to tack the extra parity blocks. For raid-z2
is a double parity scheme whereas raid-5 is single parity
(and will only survice a single disk failure).
Depending on how these parity blocks are accounted for and
your exact files size distribution, the difference you note
does not appear unwaranted.
> 2. /pool2/data2 is a RAID5 Disk Array with 8 disks, and , and
/pool1/data1 is a RAIDZ2 with 5 disks.
> The configure like this:
>
> NAME STATE READ WRITE CKSUM
> pool2 ONLINE 0 0 0
> c7t10d0 ONLINE 0 0 0
>
>
> NAME STATE READ WRITE CKSUM
> pool1 ONLINE 0 0 0
> raidz2 ONLINE 0 0 0
> c3t2d0 ONLINE 0 0 0
> c3t1d0 ONLINE 0 0 0
> c3t3d0 ONLINE 0 0 0
> c3t4d0 ONLINE 0 0 0
> c3t5d0 ONLINE 0 0 0
>
> We found that pool1 is more slow than pool2, even with the same number of
disks.
> So, which is better between RAID5 + ZFS and RAIDZ + ZFS?
>
Uncached RAID-5 random read is expected to deliver more
total random read IOPS than uncached Raid-Z.
The downside if using single raid-5 volume is that if a
checksum error is ever detected by ZFS, ZFS report the error
but will not be able to correct data blocks (metadata blocks
are stored redundantly and will be corrected).
-r
>
> <html><head><style type="text/css"><!-- DIV
{margin:0px;} --></style></head><body><div
style="font-family:"Times New Roman", "new york",
"times", serif;font-size:12pt"><DIV>Hi
all,<BR></DIV><DIV>I have 2 questions about
ZFS.</DIV><DIV><BR></DIV><DIV>1. I have create a
snapshot in my pool1/data1, and zfs send/recv it to pool2/data2. but I found the
USED in zfs list is different:</DIV><DIV>NAME
USED AVAIL REFER MOUNTPOINT</DIV><DIV> pool2/data2
160G 1.44T 159G /pool2/data2</DIV><DIV>
pool1/data 176G 638G 175G /pool1/data1
</DIV><DIV><BR></DIV><DIV>It keep about 30,000,000
files.</DIV><DIV>The content of ?p_pool/p1 and?backup/p_backup is
almost same. But why is the size
different?</DIV><DIV><BR></DIV><DIV>2.
?/pool2/data2 is a RAID5 Disk Array with 8 disks, and , and /pool1/data1 is a
RAIDZ2 with 5 disks.</DIV><DIV>The configure like
this:</DIV><DIV><BR>? NAME STATE
> READ WRITE CKSUM<BR>? pool2 ONLINE 0 0
0<BR>? c7t10d0 ONLINE 0 0
0<BR></DIV><DIV><BR>? NAME STATE READ
WRITE CKSUM<BR>? pool1 ONLINE 0 0
0<BR>? raidz2 ONLINE 0 0 0<BR>?
c3t2d0 ONLINE 0 0 0<BR>? c3t1d0 ONLINE
0 0 0<BR>? c3t3d0 ONLINE 0 0 0<BR>?
c3t4d0 ONLINE 0 0 0<BR>? c3t5d0 ONLINE 0
0 0</DIV><DIV><BR></DIV><DIV>We found that
pool1 is more slow than pool2, even with the same number of
disks.</DIV><DIV>So, which is better between RAID5 + ZFS and RAIDZ +
ZFS?</DIV><DIV><BR><BR></DIV><DIV><BR></DIV></div><br>
>
>
>
> </body></html>
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